When you stick your penis in the vagina and just let it "sit there" and PREHEAT! No slow roast, No Baking, No Broiling! No movement of any type. When you've already let the penis get to room temperature.
Derek: Hey Jenny, can I pop your cherry?
Jenny: No, I want to wait until I'm married.
Derek: Can I just preheat my dick then?
Jenny: Sure, but don't open and close the oven door or you're in trouble!
A sexual innuendo, insinuating that you want to smash.
Whaddup biiiitch, do me a favor and put that thing on preheat.