Ok so I tested some things out and I'll just explain what I found with exhibitionism
A Naked girl's exhibition stat goes up from WALKING THROUGH DUNGEONS, ENTERING TOWN and CLEARING BATTLES. It won't always go up from those things, but when it goes up it's after doing one of those things. I couldn't get it to go up from entering buildings in a town.
The stat seems to go up slower if the girl is slightly covered (topless/bottomless), so be careful with cursed armor when grinding it.
The stat becomes visible when it reaches 50. At Exhibition 95 the embarassed sprites get replaced with horny ones. At exhibition 100 they stop covering their chests with a hand bra.
UNFORTUNATELY despite having events where they don't care how they're seen, it seems that girls absolutely cannot enter taverns, the castle etc. naked and MUST at least have panties on. Which is weird when they don't have any exhibition stat at all, but doubly weird when they act embarrassed about it. So always keep panties on hand if you're like me and like playing RPGs with exhibitionist characters (surprisingly viable in this game since it means you can just wear heavier shoes, gloves and weapons). You don't spend much time in taverns anyway.
Characters resting in the inn naked will be provided free adventurer's underwear. I don't know if it's a glitch or not but sometimes at max exhibitionism they only take the adventurer's bra, no shorts. This does mean, REGARDLESS of exhibitionist stats, you can refund a good amount of your inn visit by undressing your party and selling the excess underwear you got for free.
Correct me if I'm wrong on any of this. I'd love if the tavern restriction could be lifted. Maybe with a mod...