Commonly used as a form of saying goodbye in a playful or condescending way during outings or gaming with friends.
it can also be used as a replacement for "lmao", "get fucked", "oh shit ain't no way they did that" and "welp I'm dead".
sexmaster: hey I'm going to hop off now.
CockXxTitsXx: ok zz bro.
sexmaster: zz.
Dude 1: Man they found out that Andrew stole the tennis balls.
Dude 2: zz bros cooked.