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
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!!
Someone who has been fucked/fucked up in the brain, thus making them totally stupid, foolish, or just ignorant.
A drug user...
A person who always thinks of fucking and girls.Unless his homo.
Hey that asshole is a fuckbrain!
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 !
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.