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.
"Why do you always have to be such a penis brain? All you think about is your penis!"
It usually comes with assgrabs and "accidental" boob touching, heavy flirting, and the occasional skirting.
It was okay, he was being a total penisbrains though.