A phrase meaning that some serious ass is going to get whooped, more so than usual, because there's nothing else left to do that can solve the current problem. It also makes for a great entrance to a party.
The phrase
originated from the 1988 John Carpenter film "They Live".
The main character walks into a bank with a shotgun and says the line, then proceeds to shoot all the aliens-disguised-as-humans in it. And yes, it is as awesome as it sounds.
The phrase was also used in
Duke Nukem 3D and a modified version was said in the 1993 film "Dazed And Confused", where a character says "I came here to drink beer and kick ass... and it looks like we're almost out of beer."