I was at a party over Christmas, and about an hour in I noticed a guy curled up in the hallway looking very sorry for himself. I assumed he was just drunk and left him alone as did everyone else. About two hours later I noticed that he was still there, so I sat down beside him and asked if he was OK. He told me that he had had an argument with his girlfriend and that she had grabbed one of his testicles and refused to let go while squeezing it. she had then walked off, leaving him in agony on the floor. At this point it had been over three hours since she had done this to him, and he was still in agony!
I have occasionally squeezed my boyfriend's testicles during a playfight and it seems to be agonising for him, so what this chap went through must have been awful. If this episode is anything to go by then I can confirm that this would definitely work in a self-defence situation.