A Sexual act where while having vaginal intercourse you attempt to slip your scrotum (the stump) into the vagina with the shaft (Or trunk).
Guy 1 : Hey man, I was banging this chick last night for the first time and I was trying to put my balls in her vag. along with my dick.
Guy 2 :Your an idiot, You can't just pull a stump grinder on a girl, on the first date!
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