It's his antics, what else?
It was addressed in the previous season that Toori
has to be in a constant state of happiness, or risk dying. The instant he's not happy, then he dies. I believe he's been this way since he first activated that "Unlimited Mana Works" ability the previous season.
Going nude all the time breaks any kind of ice around him, and thus helps his mood stay in the up. I know, it's stupid, but it's Toori logic
.
Btw, I forget, did the anime mention Toori's other ability already?