I spend a LOT of time at home nude. It's fun! However in a car - not sure how I would explain that to the police, so because of that I have not. BUT, BUT, I often pull my skirt WAY up so those in in trucks have something to see. And I often get some honks.
If he knows what he's doing, I prefer getting oral sex (face sitting!). But then again, if he's very, very, very energetic, doggy style sex is hard to beat.