Noun: The Thumb.
Specifically when you attempt to insert your thumb into a girl's asshole prior to having anal sex with her in an attempt to gauge how well received your cock will be.
Nate: I tried to fuck my girlfriend in the ass and she almost killed me.
Steve: n00bish mistake dude! Next time send the ambassador in first
Nate: Like a little representative for my cock?
Steve: Exactly
Paul & Derek: LOL ROFL ROFL ROFL
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