Incident in which you take a dump, and the toilet splashes you back in perineum. This is different from a regular bidet in that it's the toilet water that's splashing you, not a directed tap.
As a rule, this nearly never happens at home, and it frequently happens when you're forced to use a stall with overtly nasty waters or after you've already urinated.
person one: I'm a little worried. I had to use the portajohn at the airshow, and it gave me a spontaneous bidet.
Friend: Dude, you need to see your doctor.