happy slapping is the act of hitting/slapping someone wile recording it on a camera phone. Very popular with chavs, who think they are cool. If a chave ever happy slapps you, crack his motherfucking skull open and/or blow his head off with a shot gun. Be prepared if you see a chave with a camera phone, be ready to crack him in the jaw.
chav: hey lets go Happy Slapping.
chav 2: Yo totaley.
guy: (after being slapped) What the fuck you gonna die now, you son of a bitch (grabs knife and stabs chav in the brain through eye socket).