What do you expect to gain in doing this?? They don’t need to be told this, and telling them this is bullying. Are you actually trying to hurt them emotionally?? Because telling them this is just cruel. You’re obviously a lot taller than those you’re telling this to, and telling shorter men/guys that they “won’t have a chance” with the opposite sex all over their height is just despicable
Oh… Yeah, they’re idiots. And don’t have a clue. I think you should try to ignore them if you don’t plan on dating them. Maybe don’t have them be close friends either.
In my experience such random bullying is quite common in school. But once your grow up, such things become more rare in the adult world. Your mileage may vary. There are adult bullies and a*holes who like to pick on people. They’ll find something to tease and bait you. Outer appearance is a common and cheap way to do it.
If you’re still in school: It might become better after that. If not: Congratulations, you met some proper pricks. I hope they’re just some random people you don’t have to interact with ever again.