This is a story that is no longer an urban legend, but has now been confirmed by the attending physician Dr. William A. Morton, Jr.

WARNING: Not for the faint of heart or those with sensitive testicles...

So this guy who works in a machine shop spent lunchtimes alone, where he regularly enjoyed the sexual thrill of placing his penis on the moving canvas fan belt of a piece of machinery. One day, the excitement had caused him to lose his concentration and the fan-belt had snatched his scrotum into the fly-wheel, throwing him several feet across the floor and removing his left testicle. Rather than go to hospital, he self-administered first aid using a staple gun and then continued work when his colleagues returned. It was two weeks before he got around to visiting the hospital.

I can only hope that after this incident, he uses more normal methods like inserting his penis into a vacuum cleaner nozzle...

Read the article from the doctor