the tween version of fuck and chuck. some may literally bang someone and leave them hanging, while teenagers choose the route with their mouthes.
mack n smack refers to the action of making out with someone, and then ignoring them completely, blocking them from your life.
Mike: Yo, have you talked to Sally lately?
Bill: Naw man, I totally mack n smacked that bitch.
Mike: Good for you bro, she looks like a mack n smack.