To engage in oral sex with one or more individuals. This oral sex is generally rougher and includes "rude" or "dirty" talk. Hence the "bitch out".
Guy 1: Dude, I totally went to bitch out some girls last night.
Guy 2: Really, man?
Guy 1: Oh yeah! So many bruises.
Guy 2: Did they call you names?
Guy 1: Dirtiest mouths ever!!!! And not just the way the talked to me, if ya know what I mean!