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The insertion of your thumb into the anal cavity, using the bowling ball hand grip, nail down, in order to increase elevation of the female's hip joint while banging her doggystyle
#1- I had a dingleberry under my nail after corn thumbing my girlfriend

#2- I cornthumbed my girl for extra leverage while banging her bent over the back of the couch
by Cornthumblio November 29, 2007