When you take a towel and hold on to each end. Putting the towel in between your legs and moving it to the front and back (like you are flossing your teeth, but instead its your balls/crotch)
My balls were dripping wet after a shower so I towel flossed them.
Using the owners towel to wipe your ass after taking a shit or sharting in the motel lobby. This is a nice follow-up to the classic Curtain Floss. Towel Floss is also handy when you drop a Tub Turd.
The next time Ron went to the Days Inn at the Columbus Fairgrounds, Bob tried to fuck him over on his motel room bill again. So he ripped the towel off of his head and used it for Towel Floss.