Did that once. Seemed like everybody north of Massachusetts had a white Subaru. I was fiddling around with the key remote thing, walked right up to the car, realized somebody was coming up to it from the other side just as I noticed the stuff inside was different.

I looked around frantically and spotted my car a row over. I pointed at my car and said (lamely) "You wanna trade? Yours is cleaner." Fortunately he thought it was funny.