another way of saying just chilling. or nothin....common replies to the question of "whats up?" or "whats going on?"
the means in wanting to "get some" or have some sort of sexual activity with the opposite sex
guy1: hey yo dood? was good?
guy2: aw jus hanging brain man.
guy1: what do you wanna do mayne?
guy2: all i know, is i wanna hang brain!
guy1: k lets call some girls!