The only one I can think of currently is “retrograde ejaculation”, where your semen comes out of your testes ready to be expelled but is held in and somehow manages to go backwards into your bladder. Having never experienced this, I can’t say much more about it, but I’ve heard that it is generally not a painful experience - however, there are always exceptions to every rule.
I don’t profess to know everything there is to know about retrograde ejaculation, so I don’t want you to think I know anything about it from what I’ve said - as I said, I haven’t ever experienced it, and all I’m really doing is just repeating what I’ve heard or read from other sources. Is there anyone here who has experienced (or knows more about) retrograde ejaculation that can tell us more?