Learn English – the origin/history of “you do you” (or “do you”)

We find it in the Wycliffe bible. I quote here from the 1395:

and weren lastynge stabli in the teching of the apostlis, and in comynyng of the breking of breed, in preieris (Acts 2:42 Wycliffe)

And ech dai thei dwelliden stabli with o wille in the temple, and braken breed aboute housis, and token mete with ful out ioye and symplenesse of herte, (Acts 2:46 Wycliffe)

And in the first dai of the woke, whanne we camen to breke breed, Poul disputide with hem, and schulde go forth in the morew; (Acts 20:7 Wycliffe)

Wycliffe worked from the Latin Vulgate, in which we find fractio panis.

However, the earlier Greek has the expression too:

ἦσαν δὲ προσκαρτεροῦντες τῇ διδαχῇ τῶν ἀποστόλων καὶ τῇ κοινωνίᾳ καὶ τῇ κλάσει τοῦ ἄρτου καὶ ταῖς προσευχαῖς (ΠΡΑΞΕΙΣ 2:42)

καθ' ἡμέραν τε προσκαρτεροῦντες ὁμοθυμαδὸν ἐν τῷ ἱερῷ κλῶντές τε κατ' οἶκον ἄρτον μετελάμβανον τροφῆς ἐν ἀγαλλιάσει καὶ ἀφελότητι καρδίας (ΠΡΑΞΕΙΣ 2:46)

Ἐν δὲ τῇ μιᾷ τῶν σαββάτων συνηγμένων τῶν μαθητῶν τοῦ κλάσαι ἄρτον ὁ Παῦλος διελέγετο αὐτοῖς μέλλων ἐξιέναι τῇ ἐπαύριον παρέτεινέν τε τὸν λόγον μέχρι μεσονυκτίου (ΠΡΑΞΕΙΣ 20:7).

[I could well be mis-highlighting the second example.]

While the practice of breaking rather than cutting bread, even when knives are available, is seemingly an old one, the expression is not heavily used in pagan sources, and is in Christian sources.

Edit: Could there be an earlier source?

Well, social sharing of food is probably as old as society; mammals generally feed their young, and chimpanzees share food they have collectively hunted, so we can imagine that there was some social value to food sharing among humans from whatever time you want to start calling them human.

For similar reasons, socio-religious sharing is probably as old as religion. It's found in ancient religion ("reversion of offerings" in Ancient Egyptian religion for example), and through to the very recent (of the top of my head, Judaism, Islam, Voodoo, Wicca, Hinduism all have some form of food sharing I can think of, even Jains end Paryushan with a communal meal, and they see starving to death as the ideal way for a monk to die).

Religious associations for bread, are likewise about as old as bread. The oldest cuneiform writings include Sumerian poems which are at once myths about the invention of bread, and bread recipes: Read the myth, and you're reading the recipe. (I haven't tried these, though I have tried one of the contemporaneous beer recipes, though alas without success).

And tearing rather than cutting bread is common everywhere from ancient times to today, and from peasants to haute cuisine.

So just about anywhere and any time, can we find what is needed for "break bread" to become a turn of phrase.

It does seem though that it doesn't exist earlier in this way. While some components are pretty universal as I suggest, and some tied into specific earlier views (e.g. combining the Last Supper and beliefs of the Second Coming, Isaiah 25:6-9 was now seen by the Christians as a prophesy of a new view on the Messianic feast), it seems the particular combination of these common themes gives us the expression.

Lack of evidence is not evidence of lack though. It also doesn't help that there are biases on such matters. Many Christian sources are biased toward claiming phrasings and customs they practice to be innovations of the early Christians. People inclined to revise Christian history (quite prominently many atheists, modern pagans and Christians of denominations that don't share a particular feature) are often biased toward claiming they aren't. In practice, each are as likely to muddy waters as the other. But while I've certainly seen Neopagans pointing to the provenance of bread-based traditions to argue "breaking of bread" isn't specifically Christian (and I'd quite agree for the reasons given above, though I disagree with the assumption that modern pagan forms are entirely uninfluenced by Christian Eucharist and perhaps even by Seder), I've seen nothing to suggest that the turn of phrase is; not even some spurious cases, and I've seen a lot of spurious claims about the provenance of all manner of things from pagans.

So, breaking bread is no more exclusively Christian than breathing air is, but the expression to break bread probably does originate with the early Christians.

First sense

The Oxford English Dictionary's first sense for their 5th verb mug is:

1. intr. To read or study in a concentrated manner. Now freq. with up (on a subject, book, etc.); also formerly with away at, on at.

Their first quotation is from 1848 but I found a slight antedating from in The King's College Magazine of November 1841 (p.235, "Our School Days" by C.H.H.):

If I was industrious, I was sure of a thrashing from some big bully, for " mugging," instead of playing at cricket; if I was idle, I was equally sure of a caning from the master, for not " mugging."

Second sense

Their second sense:

2. trans. To learn (a subject, book, etc.) by hard or concentrated study. Usu. with up.

They date this to 1868 but I found an earlier example from the 1856 Aldershottana: or, Chinks in my hut:

Anon I ordered arms, and let the men stand easy, taking a leaf from Major Coolsneer's book — viz., " Let the men stand at ease ; they are thankful for the indulgence, and look upon it as an act of grace. Meantime, you are quietly mugging up on your next evolution and the proper words of command."

And from 1861's Hills and plains:

The Buffadars always prided themselves upon sticking to the regiment ; they were not like other fellows " mugging up " languages and " sucking " far and wide for staff appointments, doing all they could to shirk their duty.

Here's also an 1866.

Why mug?

The OED says the origin is unknown but perhaps related to an earlier meaning: "To pout, grow sullen; to mope." from the noun mug, a face.

My guess is it comes from having your face, your mug, close to books when studying.