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1.
When two men who have a common dislike for each other, they will in rare occasions whip out there trusty steeds and do battle.
Ex 1
Jim: I don't enjoy your company
Tim: Then lets penis fight
Ex 2
Tod: Dude you totally just took my girlfriend
Mark: You where not pleasing her anyways
Tod: You douche! Lets penis fight!
by KowasakiNinja June 11, 2010
 
2.
when two penises meet hole to hole and begin to pee on each other in a violent sort of manner. when both dicks begin to call each other mean unapeeing words. hahah get it peeing
have a penis-fight in bed
by bbboooobie mama July 23, 2009