My dad did something similar.

My parents were eating a restaurant and my dad went out to the car to wait for my mom while she was at the cash register paying the bill.

He got in the car, put his hat on, and then tried to put the key in the ignition. Key wouldnt fit. So, he was looking at his key when he realized that his hat felt really tight.

Took the hat off. It wasnt his hat!

Looked around the car. It wasnt his car! (his car was a light blue 84 Toyota Corolla. The car he was in was a Chevy car that looked similar to the 84 Corolla)

He very quickly put the hat back on the seat and got out of the car very quickly. Looked around to make sure no one had seen him, and then got into his car, which was parked right next to the one he'd mistakenly gotten into.

I laugh at my dad everytime he tells that story.