Just going to tell it here because why not.

Was at the supermarket in this very tiny town and the girl behind the counter looks very similar to someone else I know. Debated if I should say anything and finally just blurted out "hey are you related to $name?". She said "yeah she is my cousin". "Wow cool you guys look a lot alike"

Next day I see $name and mention running into her cousin.

"Haha she is still telling people that?"

"Huh?"

"We aren't cousins, we just look a lot alike so it became a running joke"

"Not related at all?"

"Nope"

Me thinking for a moment

"You are 18 and you grew up in this village, this was a little ways away and she looked about 18. So you were in different school districts"

"Yeah?"

"So how do two 18 year olds know each other so well that they have a running joke for years and yet didn't know each other from school?"

"Oh! My dad and her mom are friends. We would go on playdates together a lot when we were kids"

"Friends"

"Yeah"

I looked at her for a moment and realized that she didn't know, and decided I wasn't going to be the one to tell her.