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A person who thinks with there penis.

A guy who just wants to have sex.

A man who is horny all of the time.

A guy that thinks only with his penis and of his penis.

A man who believes everything in life can be in some way relative to the human penis.

A man who uses his penis to hide the fact that he has no skills in getting women.
"My ex boyfriend was such a penis brain, all he cared about was sex"

"Why do you always have to be such a penis brain? All you think about is your penis!"
by Suckmycockerspanielbitch69 August 11, 2008
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When a guy is being a total jerk and is only thinking on getting with you.

It usually comes with assgrabs and "accidental" boob touching, heavy flirting, and the occasional skirting.
How was your date last night?

It was okay, he was being a total penisbrains though.
by Mrs.Morphine December 17, 2008
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3
1.someone who is a freaking moron.
2. someone who thinks with his penis instead of his head.
Great job Penis brains! you spilled your beer on me!
Wow, Penis brains, you are so lame for trying to get with me.
by chasers23 July 10, 2008
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4
When you take your penis and put it in someone's eye socket
Guy: "I gave her a good penisbrain last night!"
Guy 2: "Nice one!"
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