Hmmm...Actually one of the choices in the game was to slap the guy who painted you naked. ¯\_(ツ)_/¯
Lol. Now I remember. But it was for the touching not for the painting itself. Maybe I just like hitting guys for everything >_< It just felt a bit off not to be able to throw a tantrum for guys acting strange, until Vincent did it.
The guy is a painter. It might be that painting naked people is a casual thing for him). Also he's used seeing people naked because of his abilities. I suppose he doesn't realize anymore that it's actually embarrassing for others). Just my thoughts).