To Pants someone but to pull there underwear down simultaneously weather purposely or on accident
Dude that kid got underpants in front of EVERYONE, they saw his junk and everything

Yo i was Underpantsing this and he punched me, It was a freakin accident i just wanted to pants him
by Devon K May 30, 2008
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the state of not being pantsed enough
Jock #1: Hey Jeff, check out Ben over there. He's way underpantsed.

Jock #2: Yeah, let's get him.
by foreverlong April 11, 2007
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