It's a common and fun way to make a noob angry that you're breaking the rules before you google it in front of them. I've had tough times "proving" it before Google though!
Also had that happen in a school tournamen when I was young! Nowadays, over the board I try to force it in a first game with a new person to see if they know it and if they don't take my piece, I'll bring it up to prevent it being a problem later :)
While a part of the standard chess rules for over a century, it's common for people who learn to play with their family as kids don't learn it. I didn't learn it, either, and only found out about it when I started playing chess programs online.
This is common enough that "Google en passant" is a meme in some circles.