The full form of bbeg is Big Bad Evil Guy
The definition for the slang term ‘bbeg’ is ‘Big Bad Evil Guy’.

It also can stand for ‘Big Bad Evil Girl’, depending on the situation. Popular culture abbreviates the term for a faster way to say bad dude, no matter if they are male or female.

Origin of BBEG
While social media has given birth to most abbreviations and slang terms, there are a bunch that have been created for the world of Role-Playing Games or RPGs. This term is one of those most often found in conversations about or during games. A boss or big bad evil guy is fought in battles and ‘bbeg’ is the term used to describe the situation.

Conversation Examples
Chat User 1: That boss fight was insane.
Chat User 2: OMG I agree.
Chat User 1: That was one BBEG!
Chat User 2: And his minions made it even harder.