When a person (usually a girl) snaps three times in the air in the shape of a Z. People do it to mean 'oh no she DIDNT!' or 'u got told!' It's gotta be done with a lot of attitude.
after a gay guy hits his cheating boyfriend with a purse and wants to finish off, he could do the z-snap with a little "mmm-hmm" before walking off leaving his EX boyfriend humiliated