several times hehe
i think it's more an aggressive thing or defensive. babies generally do when when they are about to lunge for your finger
My male did it to my dad and he said "Aaron your phone is vibrating."
...but also if you haven't noticed some will straighten out their tails and try to twitch them violently to show they are very intimidated.
I've had ONE wave her tail and that is my tang enigma.
She did it when I put her in the lightbox for a photoshoot.