Windish Potato 

The Windish Potato is a move to be executed only by the most skilled anal entry technicians. Though simple in design, its very nature presents serious risk to the safety of the performer's manberries and thus should not be attempted by amateurs or the unskilled. Consider yourself warned.
note-missionary position recommended_1
It consists of the following - upon achieving full penetration of the victim's slotch, the performer reaches through his own ass gap from behind and CAREFULLY places his thumb behind whichever nut he considers to be the most expendable and pushes it, as quickly as is expedient, into the victim's bungwhistle. The true danger is now at hand, for the possibility of sudden and ruinous butthole contraction is ever-present. The mark of the true potato-master is the ability to elicit moans of joy, rather than screams of pain or expulsions of gas, by using this technique. Use of lubrication is advised unless victim has sufficiently pustulent ass-herpes.

Little Timmy tried to give Jewish Jane the windish potato but found that the gap needed to reposition a nut for insertion was greater than the length of his pecker. Suspecting mischief, she unleashed her venomous couderfangs and de-balled the poor fucker right there.

Windish Potato by Dr. Gupta Gipti, Internal Med January 20, 2009