1st rule of D&D (as of 3rd edition/pathfinder): The GM is the final arbiter on all rules.
I understand this, completely, and do not disagree. That said, I'm having trouble with a group that doesn't seem to understand what I call the 'assumption rule,' which is as follows.
Assumption Rule: Unless and until the GM makes a ruling to the contrary, the rules of the game are assumed to be as they are stated in the book.
I have yet to find anywhere that it actually says this, but it just seems like common sense to me. If I cannot assume, at least for the majority of the time, that the rules of the game are as they are stated in the books we're using to play the game, how can I expect to be able to make and use a character that I made with those rules in mind?
Also, I'm not referring to one instance. This is not me complaining about a GM denying me the ability to abuse one minor loophole in the system to break the game. The group I am referring to will, as soon as anyone says anything like 'the book says,' almost yell 'the GM trumps book.' Whether or not the GM has actually said anything about making a ruling, or even disagreeing with the book in the first place.
The biggest issue I'm having with this is that, for the current campaign, the GM we have is relatively new, and isn't an expert on the rules, as they are depicted in the book. He is so used to playing with this same group, that he assumed a common house rule to actually be the rule as it was stated in the book. (The rule in question was the re-rolling of 1's when rolling stats. He was surprised when I asked him if we were doing that for his game.) This is becoming a frequent problem for me, as I play in multiple groups, and house rules vary between them. So, I'm forced to fall-back on the 'assumption rule' more often then not, only to have it blow up in my face every time I try to use a completely-legal tactic to gain an advantage in combat, or make a check that the rules say I can make, then have the group turn on me when I point that out because the GM did not specifically state that we weren't using that rule.
UPDATE: To clarify something I'm not entirely sure everyone reading this is getting, I'm not being a 'rules-lawyer.' I'm not quoting the rule book religiously, or trying to use it to argue with the GM, or anything like that. I'll do something like try to change a random NPC's opinion of my character with a diplomacy check, only to be told that I have to role-play it out. It won't be someone important to the plot, or even someone that I could potentially get some huge advantage from. This exact situation was me trying to rp my character talking the bartender into giving him a minor discount. And it was the group that told me I had to RP it, not the GM.
Or, as another example, during one combat session, I said that I was going to use the withdraw action, only to have the whole table look at me like I was stupid, except the GM who just looked confused. When they (the group, not the the GM) told me that I would take an AoP for it, they yelled their 'GM trumps rules' mantra at me just because I looked up what a 'withdraw action' is.
This is not a rant. I'm not trying to vent about something. I'm trying to convey what happened, as it happened, and ask for advice on how best to deal with this. Answers from experience would be appreciated, but I will listen to any advice anyone has to offer.
I like the group, and I enjoy being part of the campaigns they play, it's just this one issue that seems to keep coming up. I would hate for something like this to get me kicked out.
Best Answer
For someone as nomothetic as you, there is only one option: Leave.
I've been in your position. I've, in fact, written a paper (along with @CRoss and @mxyzplk) about different approaches to the rules, titled, "Clerics, Magic Users, Fighters and Thieves: Theoretical Approaches to Rules Questions on the Role-Playing Games Stack Exchange".
This group, as described, is intensely idiographic: they prefer the traditions of their group and their consensus mimicry and simulation of the "real" rather than providing for social trust through codified rules. Your question indicates that you are far more nomothetic: you don't share a mutuality of concern with them, and therefore don't partake of their particular traditions (as they claim are "house rules" but stretch far deeper into their implicit social contract). You also require external sources of imposed trust because you play in many different games.
This is exactly the position I've been in in a number of times.
The thing that will cause the least pain is for you to leave. Sometimes the right answer is, "I'm sorry, folks, but I just can't play your game." I was involved in a D&D game that I'm still bitter about, 3 years after it ended, because I couldn't make this statement. The game was playing fast and loose with the rules and the plot drove all success and failure.
Not only was I miserable, not only am I still bitter, but I count it as one of the primary reasons why I can no longer enjoy D&D 3.5.
Sometimes a game is just not worth it. If there are no mechanisms for establishing trust (i.e. everyone builds a consensus world based on shared rules or tradition) ... then there can be no ludic activities. The group will endlessly revert to "storming" and will enter a vicious negative cycle until something breaks.
Don't let that thing be your enjoyment of the game.