Def Palmetto. Elizabeth Shue is very underated, and that scene was extremely hot. I haven't even seen it since it was in theaters and I still remember it pretty well.
Now time for most awkward sex scene. I nominate the Thomas Crown affair sex scene with Rene Rousso and Pierce Brosnan. I'm 100% sure that Pierce shows his rectum in that scene. I felt violated.
edit: here's the scene from Palmetto. I thought there was more, but it's still hawt.
Mildly nsfw