Oh God
Ass to mouth and particularly rimming is not a good idea at all .. It's obviously filthy, but that's not what makes it the most gross to me. If you lick someone elses ******* and they have parasites, you could be licking up eggs - a sure-fire way to get parasites yourself, potentially even in some more dangerous lifestages than your sexual partner.
Enterobius is one of the most common parasites on humans and sit just inside the rectum.
Many who have them don't have symptoms and are unaware while some get symptoms. The symptoms then is an itch in the ass and perhaps a feeling of something moving in the *******. This happens mostly at night and the reason is the worms crawl closer to the hole itself and may even come out at night. They lay their eggs in the opening and these will surely get eaten by a potential rimmer.
A worse situation still is if the same thing happens only instead of transferring Enterobius which are annoying and gross, but mostly harmless, the rimmer licks up eggs of something like pork tapeworms. That could even be dangerous as the parasitic stage in the rimmer would not be the long worm the partner has. Instead, they get the stage which is normally in pork and can form cysts in organs and muscle tissues. There are some pretty horrific scenarios that can come from that ..
So, even if that's your thing, I think there should be a general rule that you try and keep your mouth away from people's asses.
