I think John is just hypnotized by breasts. It's the only explanation that makes sense! Especially for an episode this ridiculous.

But yeah, that was dumb and bizarre, and I'm going to go with "he didn't sleep with her" despite the stupid fade to black, because I really can't imagine him doing something like that. Still, the whole Chaya thing does provide a precedent for him acting like a moron when a woman likes him. It's just...eh. Whatever. Rodney in a tight t-shirt! Teyla's ponytail! Not thinking about it!