The only time I've ever commented on a stranger's appearance is to say something complimentary like, "That's a really nice jacket!" or "I love your shoes!"
Anything beyond that is no one else's business. What would I possibly have to gain by insulting someone at all, never mind someone I'll probably never see again?
As a slight aside, the local radio station we listen to at work has a "nooner" type show where people call in at lunchtime (hence nooner) to comment on that day's topic of discussion. A little while back, the topic of the day was things about modern life that get on your nerves. One...gentleman...called in and said he is bothered by "Huge, fat, 150lb(!!!) women working out at the gym. They're gross to look at!"
First of all, 150lbs is not FAT. I'm 5-foot nothing, and 150lbs would look fine on me! Second of all, that's what the gym is FOR! Working out, toning, dropping excess weight, getting fit. The gym is NOT for ogling women. Thirdly, I can't even FATHOM anyone thinking that that opinion is okay enough to air on a radio station with thousands of listeners. All of which the DJ (a woman, I might add) pointed out to him. She finished by saying, "Who do you think you are, judging women at the gym and calling them fat? You know what you are? You're a giant a**!" Then she hung up on him.
I am a loyal listener of her show.