he shits himself/all over the bed b/c unlike in yaoi doujins, most 'straight' men don't have magically lubed up assholes and even with 'foreplay' and 'prep' you rarely see bl doujins actually give the bottoms an enema to clean themselves out or so, and i haven't gone outta my way to find it b/c even tho there's a lot of "straight/virgin men bottoming for the first time", esp the 'drunk'/dubious consent ones, it's rare to see that happen, even in the ones where they have the 'smell' fetish or the omorashi (google the def but don't do image search if you're not familiar with that term lol) ones too, but i guess that'd turn into a scat manga
(tho i'd expect most of the 'comedic' erotica to have that happen in a non fetishy way but i imagine a lot of artists don't wanna draw that either even censored, the same way there are a lot of anal hentai oneshots too, but like i said that's its own specific subgenre of a 'niche fetish' [but i can imagine most ppl fine with reading/watching smut of it but not partaking itself b/c of the prep, plus while i'm sure there might be some women who might enjoy it, i imagine gay bottoms/some straight men would 'enjoy' bottoming more b/c of the prostate/g-spot])