To take ones penis and slap the person across the head/face with it.
Eg 1: If you're not careful, I'm going to gangster slap you!

Eg 2: She deserves a good gangster slap

Eg 3: I couldn't help it, I tripped, it accidently slipped out and hit her in the head. I accidently gangster slappap her
by Uncle Dan May 23, 2006
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