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.
Jordan: "How was your day, Hector?"
Hector: "Go to Hell, moron!"
Jordan: "Who pissed in your cornflakes?"
Hector: "Go to Hell, moron!"
Jordan: "Who pissed in your cornflakes?"
by suburbandefiner May 22, 2014