6
It’s not you. They probably think you aren’t smiling at them
I don’t know. Sometimes when people smile or wave at me, I appear to not smile back because I react too slowly
I agree with #1
I make direct eye contact
Maybe you caught them off guard? That happens to me a bit.
Interesting… it’s either you’re very ugly, but I would smile back at even a troll, so nah; or maybe they’re shy. Try talking to em.