Shorthand abbreviation for 'follow-up', typically used in electronic communication, to indicate that a subsequent discussion should occur or has occurred on the topic in question.
Person 1: "Did you want to talk about last night?"
Person 2: "Yes I did. I was hoping we could f/u on the fact your sister is stupid whore."
Person 1: "Oh yeah, bitch? Fuck you."
by T_Whatevers May 30, 2011
follow-up: to pursue in an effort to take further action
"Thanks for the f/u. I can always count on you to resolve my concerns promptly."
by Veggiecat March 16, 2007
a short way o saying "FUCK YOU" for the lazy ass people like me
by sean bucher September 13, 2004
"All Fucked Up". When something has been totally messed up. Also see SNAFU
"After breaking his wrist, his pool game is A F U"
by Matkowitz April 5, 2008
Current WWE champion John Cena's oh-so-intimidating finisher. An overglorified standing fireman's carry.
Typical announcer over-reaction:

OH MAH GAWD! It's the F-U! Cena picked him up on his shoulders, and dropped him to the ground! A lesser man would have died from such an attack!
by El Toro Grande October 4, 2005