That happened to me recently as I was entering the subway coming from a mall. And this is so unbecoming of me, but that time I was kinda moody (sleep deprived). I could tell by looking at them that they were uneducated and poor people (noticed then one of them had an old phone). I casually sat in front of them with my new laptop, put it on my lap, took out my Samsung Galaxy S4 and started playing with it on the bench in front of where they were sitting. Like hey, if you're gonna rub on my face that I'm not good looking, I'm gonna let you feel all sorts of poor while we're on this train.
Replying with the same coin is lame, but it felt good on that day to let it out. I won't do it again though, sorry.
Other than that, I don't get badly treated, but as someone else said, I guess maybe it's out of common courtesy.