look up any word, like lemonparty:
 
1.
The slightly incapacitated state of mind after a proper, vigorous fucking... and at least one orgasm.
You're under the influence of fuck brain, dude... you just asked me to MARRY you!!! LOL
by Scrappy SamCat January 28, 2009
 
2.
1. A person who impedes the flow of traffic on two lane highways by driving far below the speed limit.

2. A person who makes a stupid move while driving a car.
1. That stupid fuck brain is doing 35 MPH in a 55 zone!!

2. That stupid fuck brain!! They don't know how to drive. Look, they're all over the road!!
by Dan of Earth February 20, 2005
 
3.
Someone who has been fucked/fucked up in the brain, thus making them totally stupid, foolish, or just ignorant.
A drug user...
by Anonymous August 19, 2003
 
4.
A person who always thinks of fucking and girls.Unless his homo.
Hey that asshole is a fuckbrain!
by Gedz0rt100 November 17, 2009
 
5.
Someone who never uses common sense, like engineers and people who just don't get life.
A board is cut 1/8" short and their micromiter mind says it's off. You kindly reply "It's a house not a hydrolic pump FUCK BRAIN !

You screwed his girl friend, of course he's pissed, FUCK BRAIN !
by unomee May 08, 2006
 
6.
Someone thats been fucked in the ear and can now cum out of any part of their body because of all the cum in their head.
Cathleen is a fuck brain because she likes to get fucked in the ears.
by Dick Face March 18, 2004