How to stop giving nasty strangers mental real estate?

I appreciate all the responses, glad I found this thread again actually! I just don’t understand why strangers have to make any comments in passing, unless just saying hello to be polite, but I was going home from the shop and this guy said something like “it can’t be that hard to walk” in an annoyed tone of voice as I went by. Dunno why it was annoying for him to see, though. It’s literally just a woman walking past… Well, thanks for making assumptions anyway, you stupid dude, because actually it is “that hard to walk”. I have sensitive feet (admittedly, I should get shoes with better support rather than these flat soled ankle boots) and this path has lots of little sharp stones everywhere. I’ve also been at work all day, at a non desk job. I didn’t say anything because I always come off worse if I do, but I seriously don’t need to justify myself to these people. And I think it’s time I got plain shirts to wear outside of work (we’re discouraged from wearing our uniform tops if we get sent out somewhere). My current ones have tigers on, which strangers just love to make comments about.
Just had to rant, sorry.