As long as you don't smell like a bum.

Yeah, I had a hobby in high school of test driving whatever sports cars they had at the various dealerships in town. I didn't look like a bum but I was obviously a teenager. Worst case was the Mazda dealership that told me to come back another day before I could test drive a miata.

Most of them just let my friend and I take it out on our own, though the most expensive ones I drove were the WRX and Maxima (and the sales guy joined for both of those).

Actually, the worst was the Toyota matrix, where they didn't let me drive it at all but ride while the sales guy was driving. But that was after they let us take a celica out, possibly even because of that car being used for joy riding, since I saw others taking it out, too.