'The Wrench' is where one testicle is accidentally and suddenly trapped/squeezed by the central stiching line of your trousers, after remaining in a seated/slouching postition for too long. In sufferers this causes you to involuntarily leap forward/up whilst simultaneously blurting incomplete expletives.
The Wrench can also cause nausea and extended bruising in extreme cases involving Jeans. Also sometimes caused by excessive Gugging on hot days.
I was on the Sofa watching telly the other day. As I leaned over to get the remote, I uncrossed my legs and got a really bad case of The Wrench - I was on the floor for about 15 minutes, crying like a baby trying not to throw up. One of my bollocks is now Grapefruit sized.