[RPG] When did the word “buff” become used to describe bolstering effects in RPGs, and why

Actions have consequences

The published guidance on trouble players from the 1979 DMG (cited in @novak's answer) did not arise ex nihilo. While you can argue that there is some post hoc reasoning in this, @novak's second link shows that Gygax had strong opinions¹ on how the game "should be played." That post shows that he didn't change his views on that over the course of thirty years. His opinions were woven into this game from its origin, as were Tim Kask's once he was hired as editor of Strategic Review, Blackmoor(Supplement II, OD&D) and then Dragon Magazine.

There is evidence in early TSR material (before AD&D 1e came out) of two themes:

1. There is a proper way to play D&D. (And criticism for those not playing correctly).
2. The DM messing with the players is expected, although the original intent reads that this is in order to make the game challenging enough to be "played properly." (Full disclosure: I tend to see it Kask's and Gygax' way regarding high level characters, so get offa my lawn!)

These two themes lay the foundation for the meta action of punishing the character(s) due to the player(s) "doing something wrong."

Surprising and tricking the players

Point 2 has been with us since at least Greyhawk (probably before, given Arneson's fluid style and continuous adjustments in to his little black notebook during the proto-D&D games in the Blackmoor campaign). It arrived (p. 61-65) in the Tricks and Traps additions. There is one entry that always struck me as "meta" game (DM versus players) in origin.

Fire-resistant mummies. Many players will get used to frying these monsters with oil. but watch the fun when they run into one of these critters!

This looks like a recursive loop of player-DM-player interaction during early play, and play test, that leaked into published material. (How do I beat this guy? I'm the DM! Here, this'll fool 'em!)

There's a right way to behave at the table

Gygax and some of his co-creators at TSR had strong ideas on how the game should be played, though it was a "wide open game" from the get go. Gygax said this in his explanation of Vancian Magic (Strategic Review, Volume 2 Number 2 (7th and last SR). He addresses it also in his article "D&D is only as good as the DM." (p. 22 of same issue)

... players ... in the 20’s, 30’s and 40’s of levels ... have not really earned their standings, and their actual ability has no reflection on their campaign level, they are easily deflated (killed) in a game which demands competence in proportionate measure to players’ levels.

He alludes to DM "intervention" ...

This is not to say that you should never temper chance with a bit of “Divine Intervention,” but helping players should be a rare act on the referee’s part, and the action should only be taken when fate seems to have unjustly condemned an otherwise good player, and then not in every circumstance should the referee intervene.

The point made here isn't that hard to assess:

As the DM, you are to judge the conduct of the player and respond by doing something for the character (even if very rarely). In humans, that logic can be applied in a negative way as well as in a positive way. You can infer (@novak's DMG citation from 1979 supports this) Gygax' intent also being that you can punish a player by taking an action versus his character.¹

If "Divine Intervention" can help, it can just as easily hurt, because it is an exercise of DM authority at the table. As a principle this folds into the meta concept of the DM having authority over "how the game should be played." The rules lawyer can try to use the power of his reasoning, the DM has other sources of power at his table. It's a people thing.

How hard is it for any of us GM's (who are supposed to be having fun too) to react to friction and negative energy when confronted with it by applying our GM tools? It is not that far to go from "you aren't playing properly" to (at table) "you aren't behaving properly¹ and this is the consequence."

Dungeon Masters are entitled to a little fun too!(p. 23 of Strategic Review issue 7).

In summary, the points made in that issue of Strategic Review include:

1. There is a proper way to play this game.

2. Yes, you should use Vancian magic.

3. No, level 30 campaigns aren't the real game.

4. I'll act {fudge this dice roll} in my role as God/Luck/Fate/DM.

5. There is a proper way to behave/perform at the table, and the DM is the judge of that.

Tim Kask alludes to "the correct way to play" in various writings before the AD&D 1e DMG came out. In the Forward to Eldritch Wizardry (TSR, 1976) he latched onto the "messing with players" theme.

When all the players had all of the rules in front of them, it became next to impossible to beguile them into danger or mischief. -- snip-- D & D was meant to be a free-wheeling game, only loosely bound by the parameters of the rules. We feel that ELDRITCH WIZARDRY goes a long way toward fulfilling the original premise of danger, excitement, and uncertainty.

Kask also makes clear that there was an idea about a correct way to play D&D (campaign level perspective) as shown by his disdain for super high level campaigns in the Forward to Supplement IV (Gods, Demigods, and Heroes) to D&D. This echoes Gygax's similar sentiments in Strategic Review.

This volume is something else, also: our last attempt to reach the "Monty Hall" DM's. Perhaps now some of the 'giveaway' campaigns will look as foolish as they truly are. This is our last attempt to delineate the absurdity of 40+ level characters. When Odin, the All-Father has only(?) 300 hit points, who can take a 44th level Lord seriously?

The idea that there is a "correct way" to play D&D came across in various Dragon magazine articles (which I no longer have, sadly) and editorials under the "Out On A Limb" (Gygax) and "the Cauldron"(Kask) features in Dragon.

The "correct way to play" and correct table behavior overlap. Who is in charge at the table, and who has authority to assign consequences (punishment) for improper behavior? The DM.

Experience With Referee/DM punishment of player behavior

Table Top game referees punishing difficult players is not unique to D&D. D&D grew out of table top miniature war gaming. (Forward to Men and Magic, Book I of OD&D, Gygax, November 1973). I offer an example of a GM punishing a player in a non-D&D case of a "Hand of God" punishment. This fits the question's desire for experiential evidence. The terms "referee" preceded "DM" in the early published version of Dungeons and Dragons as a carry over from Chainmail.

My first non-D&D experience with a game referee / judge laying a "Hand of God" on a player was during a Microarmor game circa 1977, played on a sand table: Germans versus Soviets, WW II, with a few hundred micro armor vehicles all over the table.

The fight was on hilly terrain with trees, houses and obstructions (we used mirrors and other tools to determine line of sight to see if a shot could be taken or not). The captain of the Soviet team was quite the rules lawyer, something we all knew. There was bickering during almost every turn. About two thirds of the way into the battle the Sov's were up on us. The Sov captain was denied two engagements across the creek (at my tank platoon, Panzer Mk IV) based on the judge's ruling for line of sight. The kvetching went into a higher gear.

The look on the referee's face was not pleasant to see. He picked up a small trowel and dug up the sand beneath the tank platoons across the creek from me (T-34c), upending and burying the vehicles there.

When asked "What was that all about?" his response was: "Call for fire, long range artillery barrage." (IIRC K18s).
My team captain, surprised: "What? I don't have any of those units."
Referee: "The Corps Commander's Storch was flying over head, and had an artillery spotter on board. They called in the fire."

This led to a protest of course, in a tone that was acrimonious.

Out came the trowel. The Soviet artillery battery behind the farm was dug up and buried.
Referee: "A Flight of Stukas just shot up your field artillery battery."

My team captain and I looked at each other and shut up. The game didn't end well.

GM's are human, and will only put up with so much grief. To put it in a way that better fits the question, people use power in different ways and in response to different stimuli. The use of situational power by a GM when confronted with a situation that is "wrong" by a large margin should not be surprising. Given that TSR's founders cut their teeth on miniatures gaming, it would not be surprising that they had run into something like this in that portion of their hobby. This was confirmed for me in the recently released film (funded by Kickstarter) The Secrets of Blackmoor; during the first half of the film Dave Wesley reminisced about the difficulty in finding referees, how various players would or would not prefer a game with a given referee, and how Dave Arneson grew as a referee in that gaming group to where he became a preferred one. He mentioned the problem of disagreements and arguments as a part of that recollection.

¹ The second post in novak's answer:

... I recall composing those admonitions...and I note my expression was "Blue bolts from the heavens," implying as I suggested earlier lightning from an angry deity.

As a matter of fact I did not use them but when a player or players became obstreperous I simply rolled a d6 and informed the miscreants that their PCs had suffered that much damage. Unless they wanted more of the same, all misconduct had to cease. I did roll several d6 damage for a couple of very unruly and rebellious young players. When asked why their characters were taking such damage, I said because they had offended the rest of the group, me in particular, and if they wished to play further they had better note the damage, be silent, and mind their manners.

They did just that.

The Judge's Shield (1977) predates the Dungeon Master's Screen by about two years, give or take some months. (That the Judge's Guild got to this first is not surprising, as Gygax infamously told them that nothing but rules would sell, and the Judge's Guild was fated to prove him wrong.) So the term “shield” was established before the term “screen”, and still has minority currency today.

The Referee Screen (1979) for Traveller has the same vintage as the DM's Screen and is the only other data point before the 80s begin. It's unclear which was published first that year and therefore which one coined the term “screen”, but together with their two popular games — D&D and Traveller — they certainly had a large enough combined audience to establish the term “screen” in common usage over the the term “shield”, and likely TSR's audience alone would have been enough to establish the term as definitive. (Judge's Guild material, although designed for use with D&D and acclaimed at the time, was not “official” and that would have prevented a lot of play groups that didn't stray from TSR-branded material from being exposed to the alternate term.)

The history isn't very interesting, unfortunately. The only reason we have more than one word for it is because “shield” enjoyed first-to-market advantage in establishing mindshare enough to not be completely destroyed by the TSR juggernaut's adoption and promulgation of the term “screen.”

The “GM Screen” variation, as noted in the other question's answer, is merely a variation of the term that follows the separate trend of the hobby adopting “game master” as a non-trademarked, non-D&D-specific term, whether out of a hobbyist's need for precision or a publisher' need to avoid legal trouble. The term “GM screen” therefore doesn't have much of an interesting history of its own. You can see “GM screens” in a few early items:

• The Morrow Project's Game Masters Shield and Reference Tables (1980)
• The Star Trek Gamemaster's Kit (1983) including a “Gamemaster's Screen”
• Avalon Hill publishing the RuneQuest Games Master's Screen (1989) for RQIII