Based off That Scene in Witness (actually, there are a lot of those...)

Luke still isn't comfortable with immersive water bathing (it feels like a waste, after spending so much of his life conserving every drop) and instead regulates himself to sponge baths when a water supply comes in.
He's stripped down in the Falcon's hold, water glistening off his skin and dripping from his hair, when he turns and notices Han watching silently from the doorway.
All the sexual tension that's been building since their first meeting comes to a head.