Summoning the monkey

Summoning the monkey: a euphemism for masturbation.

Originally coined by Liam O'Brien of the Critical Role D&D ensemble, and subsequently (maybe) made canon by DM Matt Mercer's explanation that summoning the monkey is the past time of many a wizard in their early years of training.

Sam: Have you seen Liam?
Laura: He's in the bathroom, probably summoning the monkey.
Sam: Thanks, I think I'll join him.