I remembered this article in chil chil, they have all kind of articles like that ╮( ̄▽ ̄)╭
https://blnews.chil-chil.net/newsDetail/12580/
If you reach deep enough, you’re literally penetrating someone’s stomach — like that’s the “barrier” a top breaks into.
Kinda gross to think about but think of it like if someone pushed snot up your nose, how would your body react to that organic matter being shoved inside you?
There’s also the matter of whether the person penetrating actually has a big enough dick to penetrate your stomach so it really is a case by case basis
specifically it's entering the sigmoid colon. there isn't a sphincter there and nothing is breaking, it's just a 90° turn at the end of the rectum.
I find this trope extra funny with the knowledge that SK has like.... not only the smallest dick sizes generally but also one of the larger discrepancies between claimed dick size and studied dick size. make of that information what you will lol

Can someone please explain to me this “if you don’t wash out the cum I your ass, it’ll hurt your stomach” thing that I’ve seen multiple times in manga? Have never been able to find anything scientifically or medically to really back it up, doesn’t seem to be a thing irl either. So why is this line so often in yaoi? It’s weird