In college, I once actually unlocked “my” car with my key, got in, and looked around confused. It wasn’t my car. Same make/model, but it wasn’t mine. I sheepishly got out and found mine on the next row.
But that wasn’t as bad as when my H picked me up after work one day. I walked down the steps, into the car that pulled up, looked at the guy driving who said “who are you?” Oops. I got out and slunk away…
Many cars had only a small number of possible keys, so finding another car with the same key did happen.
Congratulations! I just bought my very first ever brand new car in July. At the ripe old age of 50 
As far as crazy or spontaneous purchases…instead of buying my D a cheap IKEA dresser for her college apartment I decided to give her my “vintage” piece (bought at a thrift store for $30 back in 1997) and I upgraded my own to a grownup one (read: big, new and stylish). It’s arriving on Monday!
That’s such a great feeling. I have my 40 year old dresser here at my house with me… I upgraded it a few years ago to an “expensive” Ikea dresser, Lol. Both are real wood, but my Ikea one is much larger and more modern looking. It was also > $200, so definitely not one of their cheap options.
I had a teacher once who hopped in the car at the grocery store and drove off. But it wasn’t her car…