The correctly spelled contraction for what's up.
Hmm...I don't know what to say 'sup yo!
1) The brief way of saying: "Hi, I'm really pathetic, what are you doing?"
2) Probably the worst response to any humane or initial greeting.
3) Okay if used when your under the influence, jocularly, and/or feel the need to be obnoxious for one hot sec.
1) Man sitting at bar with Corona: "'sup"
Woman trying to get a drink: "Oh! *Smacks forehead* I'm so sorry, but I don't understand all of the one word you just asked me or if it even if was a question at all"
2) Kind girl texting boy: Hey :) What's up??
Boy one hour later: "'sup."
3) Drunk tourist in cab: "Man, you do understand how epic tonight's gonna be, right?"
Hammered tourist friend: I know, dude! ETA 15 minutes... SUUUUUUUUUUUUUP ATOWNNN. We're about to Get It IN!