John Cena's finisher move (came before the STFU).
He came up with this name when he was in a fewd with Brock Lesnar, whose finisher move was the F-5.
Also an abbreviation of 'F*** You.'
"Yo, Brock, your finsher's the F-5 - well, mine's the F-U!!
Person 1: (gets nudged by bypasser) Aww, F-U!!
Bypasser: Dammit, just say the word man!