A twat that twitches, unprovoked, at random times throughout the day. Twitches can vary in duration, and intensity, and can be a source of extreme pleasure/discomfort to the owner of said twat.

When you eat dirt for the first time and leave your family to build a shack in the woods

A twitchy twat is to a woman, what a hard on is to a man. Just as a man's penis gets hard when he is aroused; a woman's clitoris may twitch (multiple times in some cases), in response to her own arousal. The twitch is often in response to that which has aroused the woman.