Can someone tell me why this is offensive

I’m sorry if this comes off as ignorant but I really am curious about this

Why is it considered offensive when someone tells you to smile? I genuinely really am not sure why this would be offensive. I mean no one has ever actually told me to smile before so maybe if I had gotten that, I feel like I would probably be annoyed, not offended. Or if someone told me “smile you look better” I could see how that could be offensive.

I saw a meme today and it said something like oh because of the masks no one has told me to smile, and a lot of people were in agreement and I was just like what

Has anyone ever asked you to smile before? And if you were offended, why?