Re: Oh, go on then
If you have bladder stones you maybe unlucky enough to have a doctor stick a camera into your bladder to have a look. They use an endoscope (technically a 'cystoscope') that's about 3-4mm diameter.
Barring surgery there's only one way that camera is getting in there, and, yep, everyone reading this just involuntarily tried to cross their legs. As a man, one of the worst bits is when they have to get it round a narrow corner right by your prostate.
Definitely one of my least favourite medical memories, although I did get to see the inside of my own bladder, which I suppose few people can say.