A slap to the face, often from male to male, used sometimes to intimidate, anger, or irritate. Mostly, however, this term is for quick revenge for someone saying something dumb. At the same time, the word "dummy!" is shouted, characterizing the victim.
1: First Person: I rammed your momma last night. Second person: Dummyslaps!
2: I'll dummyslap you!
3: You dummy. *Slap*