Why do adults always tell me to smile?what the hell?

i have a unique style, kinda like punk so peopl mistake me as goth a lot, but i laugh all the time, im a really funny person. but ill be minding my own business, and them usually someone like a teacher will be like "hey can you smile for me?" which pisses me off, cause i can just tell they think im some freak who never smiles. and today, i was walking to my locker from cl and this old teach er guy stopped me and was like "hey, i had a bad day today. can you do me a favor and smile?" and i had no choice but to smile, cause i couldnt just run off since we were the only people in the hall so i did. but it pissed me off cause i knew he didnt have a bad day, and he just said that to get me to smile. but that makes me so mad, cause adults always do things lke that to me and im like "okay, so am i just supposed to constantly smile?" and my docters a real *****, and the one day i wore a black hoodie and i was acting pissed cause she was being an *** and shes like "okay, are you depressed? cause youre acting like it?" and i was just like **** you!