to grind one's groin against someone's booty while dancing, usually while moving in time with each other. possibly while tapping dat ass and simulating sex.
"everybody in the house. i wanna see you work up the sweat. if the person next to you don't have a sweat, hit the door"
A metaphor for: "I think you should leave. Do not pause or delay while you are leaving." Generally used when the addressed has been complaining about circumstances that the listener doesn't agree with. It comes from a time when doors were on spring hinges and if you paused in the doorway while exiting, the door would spring closed behind you and hit you on the backside.
"This place stinks. I am too qualified to be here."
"Well, don't let the door hit you on the way out."
This means the same thing as, "Beat it," or, "Get the hell outta here," or, "Yeah, the door is this way, pal."
When Wayne's job interview was going poorly and he had a fight with the interviewer, the interviewer kindly asked him to leave by saying, "Yeah, Don't let the door hit you on the ass, buddy."