"The Price" from TNG. Troi beds a negotiator and they're rolling around in bed, and then Troi straddles him and starts rubbing some oil on his chest.
I always thought TNG was pretty tame but this scene would stand up against the best of them.
Easily.
Also one of my most embarrassing moments as a ten year old child. I'd been telling my mother what a great show TNG was and she agreed to sit with me one week to watch...