to rob, bully, or verb someone. No matter what the case, frontin on somebody always has something to do with confronting them in some way. It comes from the word front, which means acting like something you aren't. So "fronting on" somebody is basically trying to make yourself look greater than you really are at the expense of that other person.
C.L. untouchable, with the clip full / Impossibly, the posse can't front on me!