I know there are risks for person doing unprotected rimming but are there any for the person being rimmed? Is the person's mouth bacteria dangerous fire the tender lining of the rectum?
Definitely much lower but I'm still wondering if bad Bacteria could be introduced. I would also think herpes can be spread to receiver.
Bacterial infection from mouth -> anus is very unlikely as your mouth flora is relatively harmless. Herpes, yes. HPV, yes.
It depends what you mean by dirty. I don't know how it compares to a dog's mouth, but our mouths are home to a lot of bacteria. The stuff that normally lives in our mouths are harmless to us though, even if they are shared with someone else, and they aren't going to cause any trouble if they are introduced to your butt.