What is your reaction to total strangers when they say "smile!"?

i’m not exactly sure what expression i have on my face when i am doing simple things like walking, working or paying for groceries in the “15 items or less checkout.”

i could just feel this cashier looking at me as i retrieved my grocery items out of the shopping cart. she finally said, “you look so mean.”

i’m thinking to myself, “no, i’m just putting groceries on the belt—is there a need for me to smile or be chatty?”

it’s not the first time i’ve heard this remark, but i think it has a lot to do with my eyebrows and also my genetics that come off stern-looking, but i’m really a nice guy, actually.

are you offended when total strangers say “smile?” what is it about your face or demeanor that gives people the wrong impression?