A term used to talk shit about a guy that can easily lay your ass out. SJ's are typically roid raged douche bags that think they kick ass although after high school they'll be working as a janitor. Often heard making animalistic grunting noises.
Guy1: Shit! dude SJ heard us!
Guy2: Fuck now he's gonna whoop our asses
SJ: Huh! Why the fuck are you doing that shit?