Well, truth be told, you have in some kind. Ever smelled a fart? Do you know how smelling works? Molecules from the air come through your nose and are distributed in your mouth, where they settle on the receptors of your tongue and you taste these molecules. This is called smelling. So when you smell your own poop, it's because molecules that were previously in your ass have passed through the air into your mouth. If you smell your bro's fart, it's because he has figuratively shit in your mouth. At least enough molecules. So to come back to your statement: yes, you've had shit in your mouth often enough in your life. Not directly whole morsels, though... I don't know you. Maybe you have. No kinkshaming on my part.
Yes, really. Nature is amazing, isn't it?
But it is completely avoidable for the younglings who can't handle adult stuff. Ingame you just have to avoid doing stuff you aren't strong enough to handle. The best way is not to have sex with the LI's. Then there's another way to avoid it. Just don't play an AVN which isn't intended for people of your age.