First off, this is not actually my story but my dad's whom asked me to post when I mentioned this subreddit. Second, this is over 40 years old so that may be relevant but really means there's no need to recommend they break up. Yes, English is my first (and let's be honest, really only) language so mistakes are entirely on me.
Let's call my dad Pete and my mom Linda.
When my parents were dating apparently early on (this is currently being debated by them and is either a few months officially dating but knowing each other for a few years or back together after a long distance break) Pete told Linda he was getting her a rock for Christmas and that she would love it.
So Christmas comes around and Pete gifts Linda a fossilized fish (so not technically a rock). Linda starts crying which confuses Pete as this was a really well preserved fossilized fish. He decides to ask Linda's friend, Emily, why. Emily told him Linda was expecting a diamond which was an epiphany for Pete as apparently he didn't realize how serious Linda actually was about the relationship.
For background Pete's parents owned a rock store (think geologists/archeology not jewelry) and he collects rocks. Linda also loved (actual) rocks (she was a science major) so there had been previous rock conversations (?).
After the rock that's not a rock, Pete asked his parents to go to Linda's parents to assist in showing his commitment which helped smooth out the miscommunication.
Back to current day, Linda still thinks Pete was a bit of an ass for telling her to expect a rock for Christmas but instead gifting her a fossilized fish, even if it is cool looking. Pete thinks the rock was an awesome gift and that telling her to expect a rock didn't automatically mean a diamond.
Is Pete an AH for telling his then girlfriend he'd get her a rock for Christmas?