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2.
The act of making yourself cum while simultaneously dropping a deuce.
My girlfriend wouldnt give me a blumpkin because apparently she hates the smell of my deuce, so I went into the bathroom and gave myself a jumpkin.
by usmc_nightmare March 25, 2010
 
1.
Much like a blumpkin where you get blowy while dropping off a SEAL team, its when you jack off and take a shit at the same time because you're stuck in some third world shithole or... your parents house.
dude 1 walks into the bathroom
dude 1: hey man, hows it going? you've been in here a minute.

dude 2: it was going good until you interrupted my jumpkin
by 9223-beotch April 03, 2013
 
3.
Jacking off while fingering your butthole, with the result being intense sexual pleasure.
After Pat's underwear were frozen, he sat in his room and gave himself a jumpkin.
by jackinit April 03, 2005