1. Greeting to someone. A way of saying "hey what's up?" origniated in Detroit.
2. Can be used as a term of aggression to entice someone into a fight or altercation; Bring it on...
1. Guy sees his buddy and greets him with " What up Doe?"
2. Guy 1 walks into a bar with the mean mug, staring at guy 2. Guy 2 throws up both hands and says "What up Doe!?"