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Someone who can't help but to fuck up whether they are natural at it or just an ass. Sometimes it's unsuspecting. It also can just be someone who fucks up by saying the wrong thing. A Fuck Up can either be a good person who is pretty damn accident prone by default or just a dipshit.
The following is A Fuck Up who says stupid things:
Donna: I love you.
Eric: I love... cake.
by AP Fuck Up April 15, 2009