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!"
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