The equivalent of blowing bubbles on someone's skin. This produces a "farting" sound and tickles the recipient.
This term was coined by Bill Cosby during an episode of his sitcom "The Cosby Show" where he and Keshia Knight Pulliam discuss the meaning of several abstract words she is trying to spell.
See also zerbert (same as zrbbt, spelled with vowels)
See also raspberry
Pull up your shirt so I can zrbbt your belly.