
Anger increases bloodflow which would also increase certain parts of the body

I think any guy in love, will be perverted when they're with the one they love. It might not even be a question of getting the urge to do it, but maybe something psycological? For example, when the seme finds someone else's kiss marks on their uke (or the other way around, in some cases), the seme feels like he needs to make the uke his own again, by having sex :)
Not sure if that's the case here, though. Actually, I think he might be trying to avoid the "Sempai-subject", by taking up on the uke's offer, which he obviously benefits sexually from, as well (⌒▽⌒)

Superb logic!!
Do guys really have the urge to have sex when they're mad? Just been going on also with other mangas