hump your fist:

Of a male, to masturbate . See masturbation-male for synonyms.

Quote: Vince (Tom Cruise), a pool hustler , and Carmen (Mary E. Mastrantonio), his girlfriend putting a stop to his winning streak in The Color of Money (1986):
-- Vince: ' Carmen, I'm playing here! '
-- Carmen: ' Yeah! I know! Listen, you win one more game you're gonna be humping your fist for a long time. O .K. Vincent? '

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