The word you say whenever you see a Smart Car and follow up with a palm push/hit to a person's body, preferably on the head. It's similar to the idea of a "punch buggy" or "slug bug", but in a newer version.
Person 1: (sees Smart Car passing by) Smart smack!
(palm push to Person 2's forehead)
Person 2: Ah, you got me there! Ouch...