I didn't really associate the stereotype of bad teeth with lower class British people. AFAIK the stereotype comes from even rich British aristocrats supposedly having bad dental care.

That said, you are right that applying that stereotype to specific people without first checking if they're upper class is more likely to hit lower class people, especially with how culture has shifted since the stereotype was first formed.

We don’t associate this with class, we think even your rich have fucked up teeth.

Who said they were bad? That's on you. I love a snagle tooth 😍 so many people straighten their teeth unnecessarily. It removes all their character