The bloodynose gag was the only one I could not accept because it became a plot point. At least for a long time. I've sensed used logic to force my brain to accept it.
Sanji not being around women for 2 years, caused a build up of sexual frustration and tension with no release. So when he did see them, the frustration caused his blood pressure to sky rocket but instead of causing a stroke, due to his durability it instead just ruptured smaller arteries in the nose, being arteries they still were dangerous if left alone, and thus life threatening.
That's the only logical explanation and I'm sticking to it so it makes sense to my mind.