It's an acronym, "Bring your own beer." Mainly used as a code word on texts, computer, etc.
Ryoma: I often think that soccer games in America relate quite well to hardcore Mexican burrito parties because they are both words we use that have different meanings in different countries. Get it? Like BYOB in Mexico means "Bring Your Own Burritos," but down here it means "Bring Your Own Beer." Hahahahahahaha. Get it? Get it? And how like America calls it soccer but the rest of the world calls it football. God damn man. That's some crazy shit i just realized. Damn. Hahahahahahaha. huh?
Mac: ...
Ryoma: Do you get it. huh?
Mac: *drag* *drag*
Ryoma: YO MAC!
Mac: What the fuck do you wunt!? WHAT!!!
Ryoma: Oh, do you get it?
Mac: Brah! Shudup erredeh!
Ryoma: :(
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