Mitch: (in a meaningless argument with the person next to him while the rest of the world tunes them out) No, I'm positive it isn't done that way. Right Al?
Al: Who shot who in the what now?
Idiom meaning "Why are you in a bad mood?", implying discontent with the other person's attitude. As it is a rhetorical question, no response is expected. Often used in situations where the person being asked is angry as the result of an underlying cause and therefore snaps at people who have nothing to do with this cause.