A (sometimes playful) smacking of someone's (usually) clothed testicles.
The bitch walked a little too close to me so I gave him a wicked nut tap!
An attack made with a somewhat playful, somewhat malicious intent on the nuts of a friend or acquaintance. A "nut tap" is generally delivered with a hand (and most often the back of a hand with a flicking motion) but may be substituted with any object (i.e. water bottle, car keys, cell phone, text book etc.)
The "nut tap" does not however come without risks to the "nut tapper." The risks to the "nut tappie" are obvious, however the "nut tapper" risks being ridiculed as a "fag" (or queer) by the "nut tappie" if the "nut tap" is unsuccessful. An unsuccessful "nut tap" resulting in contact with the "nut tappies" shaft and/or head in the instance that there is no contact made with the "nut tappies" nuts.
Arion: "Shaun, why are you laying on the floor in the fetal position?"
Shaun: "Jason just nut tapped me with his water bottle..."