An underdeveloped person of low mental capacity, and value compared to others of the same kind. Much as a tadpole is just an underdeveloped, and lower level of a frog.
"I have this huge tadpole in my Spanish class, and I can't tell if he has autism or not."
Attempting to give someone (most likely a male) the Shocker but unfortunately the pinky is left without an orifice, thus wiggling around like a tadpole.
The gentleman was unaware that he had accidentally given the woman the Tadpole rather than the much desired Shocker.