Yusuke is a huge fan of nudity. At one point in the original game he visited the protagonist's room and complained of the heat:

Yusuke: You should buy an air conditioner.
Rei: Just take your clothes off.
Yusuke: Why didn't I think of that? It's decided. I'll live my life wearing as little as possible.

(The 'take your clothes off' suggestion also earned me a bunch of affection points with him.)