Nerdy: grab dice and char. sheets (yay!)
Sexy/Nerdier: Skill check, have in character sex!
Sometimes it turns out hot and surprisingly natural. Sometimes it's disastrous.
As for non-nerdy based bedroom RPing, I'm not sure I've ever done it. I don't think I can really stomach "okay you're a cop and I'm trying to get out of a speeding ticket" without a well-written character back-story #_#. I might be too nerdy to live.