Why do boys boys stare at girls when they are putting on lip balm, lip gloss, lipstick?

I was putting on lip balm and this boy wouldn’t stop staring at me until I stopped so I ask my friends and they said it happens to them I also saw a tweet about it and all the girls responded it also happened to them. So why do boys do that? It’s quite uncomfortable
Why do boys boys stare at girls when they are putting on lip balm, lip gloss, lipstick?
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