The “tail snap” occurs after you say something sassy, and is done by popping your hand by your “tail” and snapping your fingers. I first saw Cecilia tail snap someone at a party, which, by the way, is a perfectly acceptable place to tail snap someone. The moment went a little something like this: Random guy strikes up boring conversation with Cecilia and she tries desperately to escape, to no avail. Then, a perfect opportunity presented itself. Random guy brings up that he is a graduate of the University of Georgia. Cecilia, who didn’t miss a beat, shakes her head and says, “Well, sweetie, I’m a Tech fan, so I think we are on opposite sides of the hedges if you know what I mean.” Tail snap. Exit.
It was genius.
I, however, have taken the tail snap a bit far, as I did it to a co-worker last week. We have just moved into a new office space, and not all of our offices have doors now. A male co-worker of mine locked himself out of his new office (yes, he got a door and I did not) and we had to call a locksmith to get him in. As he worked in the conference room for the day, I sassily told him, “Well, guess what? That’s what you get for having a door.” Tail snap.
He looked confused. I quickly scurried back to my desk, and have decided that it might be best to leave the tail snapping to Cecilia.
thetightropeblog.com 
Ok – I'm having a hard time getting the exact movements of a tail snap figured out – is it a snap, and THEN an ass slap? A snap and simultaneous slap (which is hard, because i"ve practiced in my office with a door just a few moments ago). Or a slap and THEN a snap? I just want to get it right, since nothing says masculine like a tail snap…
You are so right. Nothing says masculine like the tail snap.My description could've been better, but there is no slap in "the snap." You place your hand near your tail by extending your arm downward (with sassiness, hence why I said "pop") and then…snap. I hope this clears up any confusion. Best of luck, but please, use with caution.
Tail Snap Caution: use only while witty. Tail Snap often causes backlash leading to a sharp tongue of strangers or passers-by thinking tail snap was aimed at them. Must have proper comment ready to aim and fire.