It's not weird, it's unhealthy. And I'm saying this as someone who is a firm believer in equal beauty standards/freedom of choice, not someone who believes all women should wear makeup and nail varnish etc.
If you don't brush your teeth, they will ache and eventually fall out.
If you're like me and the problem is that mint toothpaste tastes disgusting, there are other options out there including for adults. I'm using a liquorice one at the moment. It tastes nicer so I'm more inclined to brush my teeth than having yucky mint flavour in my mouth.
If it's a routine thing, try to build it into your routine somehow.
If you really can't do it then look into a sugar free diet but that's basically impossible nowadays so it would be far easier for you to just go onto brushing twice a day or at least once a day.
End of the day though, it's your own choice. Just be aware it's about health/avoidance of pain rather than simply beauty.
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Not actually a girl
He/him