Hello!

I had read this one yaoi (oneshot?) where the mc was still a virgin because his thing was too big and he gets bothered by his neighbor (bottom that sleeps around)

The next day they switch bodies and the mc is telling his neighbor to not do anything in his body.
Later they have sex and switch back and it was found that the neighbor because a bottom because he had the same problem as the mc.

Chap 6 of Kuro Ouji no Iinari ni Naranai! ?

omg yes! thank you so much.