I had a red 1962 VW Bug in high school, when they were everywhere. I came out of work one day, unlocked my door, and started it up. I reached over to turn on the radio and had a weird deja vu-like disorientation as I realized that it wasn't my aftermarket stereo. Then I started looking around and noticing some other small differences (mine was mostly stock). It only took a few seconds to realize it wasn't my car.

I quickly shut it off, jumped out, and locked it up. I took a nervous look around to see if anyone thought I was stealing their car. Whew, nobody around. I then saw my car (I checked the plate number this time) just a few more spots further down the row in the parking lot. That was certainly an odd feeling. I guess those old VW keys weren't all that unique. 😀