Top definition
When a male wears boxers and their penis pops out of the hole when they walk around with a boner.
Dude:dude, i had a boner watching underworld and got up to go get a drink, bad idea.
Dude:cause it was a penis-in-a-box waiting to happen.
OtherDude: o shit! good thing i wasn't there!
by DaRTH TaNK May 31, 2006
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