Do you think vampires, with their heightened senses, are more susceptible to pepper spray? Like, I was thinking about how Bella has a can and just wished for Edward to scare her one day and she whips it out on him and he doesn't expect it and is just...he can't even really cry to get it out of his eyes!
I have no idea! I would assume whether it would be painful would depend on whether their senses are still capable of being affected with pain by certain irritants. I can't recall anything similar with touch, so I'd base the effectiveness off of their olfactory senses.
We know their sense of smell is super heightened when it comes to prey/blood/other supernatural beings, but I can't remember if it's ever established whether they're able to detect smells from things like plants or normal food the same way. I think it was and they do, but I also think Smeyer might've said that food tastes like nothing to them at some point? And sense of taste and of smell are really tied together.
Based on that, I'd say within Twilight canon, that pepper spray would have a very significant effect on vampire olfactory senses, but little to no physically irritating effect on their 'flesh'. It could cloud their vision but not incapacitate them, at least not through pain. They'd have to wash out the substance with an external source of water, but other than that, it would probably just leave them nose-blind for a few hours, maybe even a few days depending on the actual contents.
However I in no way respect Smeyer's word of law, so for me personally I'd mix in some WWDITS rules. According to Mr. Waititi and Mr. Clemmons, vampires, as well as having heightened smell, can taste normal food, but they cannot subsist on it because eating induces immediate and extremely violent vomiting. I would assume as this is any body's way of rejecting poisons, that normal plant, spice, dairy, meat, and grain-based food or the nutrients contained within are somehow toxic to vampires. (This jives with the idea of vampirism being a sort of medical condition that I love!) Again, this is WWDITS rules, not Twilight, but I'm blending the two a bit for my own pleasure.
Using these rules, not only could Edward be painfully blinded, both in his eyes and his nose, but he may end up literally sick! So that's fun!