The act of two individuals rubbing their buttholes together in a misguided attempt to achieve sexual pleasure. So named for the involuntary noises and facial expressions made by the participants during the act.
Person 1: Guys, I tried the Grumpy Troll last night.
Person 2: Seriously? Feel anything.
Person 1: Nothing. Literally, nothing.
Person 2: How hard did you try.
Person 1: Let me put it this way. I'm much grumpier today.