What BYOB means? Be Your Own Baby? lol
The usual use of BYOB is in informal invitations to parties, it's a shorthand for "Bring your own Beer" or "Bring your own Booze" meaning that the alcohol at the party won't be provided by the host and if you want to drink you should bring the alcohol yourself. BYOB can also sometimes be used in party invitations to mean "Bring your own bitch"** to say there won't be a lot of women and you shouldn't expect to "pick up" any girls there.
**Bitch literally means female dog in English, but is usually used as an insult against women who are seen as too aggressive, overbearing or cranky. In this case it simply means "girlfriend" or "wife" but may still be viewed as offensive and sexist by suggesting that all women are "bitches".