the act of sticking one's thumb into a post-coital anus followed by removal of the thumb, now covered in mixture of feces and semen. then forcibly thrusting the thumb into the mouth of the unsuspecting partner. this technique can also be used to mark the partner's body, or any surface of the surrounding area (ie. wall, bedpost, partner's back).
my life partner gave me a tough gumbling last night.
i screwed joe last night and totally gumbled his new nikes.