YTA

A lot of responses didn't read the question. This isn't about the bed or the joke: this is about telling people a very private thing about her to retaliate for her overreacting.

Absolutely that was a rotten thing to do.

The bed joke was silly. There are lots of ways to tell kids about noises without explaining sex. You're not an asshole for sending that text.

But you're 100% an asshole for telling that private, embarrassing story about her. What a petty, awful thing to do when someone was just petty and awful about you. Come on. Be the bigger person. She was wrong, but you could just hold your head high and move on. Telling that story was what makes you the asshole.