Most Helpful Girl
It would be a turn-off, but if I was doing his laundry, I'm assuming that we've been together for a decent amount of time? I mean, I've only done my boyfriend's laundry after we were living together.
If I liked him and we had been together for some time, I doubt I'd break up with him. I'd probably bring it up to him though, especially if it wasn't a one time thing. It would suggest that he has some hygiene issues, and additionally, if he's not wiping himself well enough, I'd be concerned that it might be smelly to go down on him (since my face is fairly close to that area).
1. Shower regularly.
2. If your undies get stains in them, buy new ones.
3. If you find that skid marks are a frequent issue for you, I'd suggest investing in some flushable wet wipes. When you take a poop, wipe first with toilet paper, then wipe with a wet wipe to make sure you got everything.1