I think all you can do in that circumstance is ignore it. Had you challenged them, and they were in a group, they’d quite likely have taken it as a come-on and an excuse to behave in an even more boorish way. They sound like young (I hope they were young), ignorant and disrespectful fools, who supported and egged on by being with their peers behaved like morons. I’d guess if you got one of them on their own, they wouldn’t behave like that or admit to behaving in that way. Perhaps you can film them on your phone if you come across them again and share on Facebook.