What are some of the worst comments, or notes on character that a stranger can say to you? What is the worst "advice" given by someone you don't know, at all, or very well?

I have two.

"Smile." You don't know me. You don't know what I'm going through. Someone could have just died. I'm glad you are so happy-go-lucky that you are enjoying your day, right now, but when it turns to shit, how about I come and piss on your face, and then tell you to "smile."

"You're still young." Well, well, well, how fucking young am I? Do you even know? I am young compared to you, for sure. "You're still old, and getting older." Eat my sperm, bitch.