Stands for What Is Fucking Wrong. Used when someone nags a lot and you just want to tell them to get to the point. Also used when something weird happens and you don't know what is going on.
Guy 1: Dude, I am soo mad.
Guy 2: You have been mad this entire week. Now STFU if you won't tell me WIFW.
*The day after the BP oil leak*
Guy: WIFW with BP!!!