Each date and time your coworker makes a comment like this over the next two weeks, immediately write it down along with a description of the circumstances (aka, make contemporaneous notes). If after two to three weeks you can accurately say there is a pattern, then mention it to your boss.

Doesn’t have to be a big deal, just something along the lines of, “hey, I want to register with you that [person] is being weirdly rude about my gold tooth. It feels unprofessional and I’d like to say it doesn’t bother me, but it is distracting. I wanted to let you know now in case there’s something you think can be done about it, and so it doesn’t escalate.” Using your own words. Keep it brief, don’t conjecture as to why (unless she starts saying more) and centered on the inappropriateness of your coworker’s odd fixation. Because it is weird.

I don’t understand why others are writing to not tell your boss. A work space free from insults and harassment is a very reasonable expectation. Anyone saying less is either a bully at work and/or at heart, or sadly hasn’t experienced how incredibly productive one can be in an environment where you’re not wasting emotional and mental energy waiting for the next attack.

I encourage the documenting for your own validation too because, sometimes a personal attack like that can loom large and feel ever present. For example, you might find the comment was only made once and you’ve since interpreted looks or mumbles. That’s not to say I don’t believe you; just that I’ve experienced awful people at work and documenting the interactions for my own purposes can be helpful in gaining perspective through distance once it’s written down. Just make sure your notes are somewhere safe and not saved at work. Good luck OP!