How do you deal with casual hate speech from people you know?

So, I have some acquaintances who are very religious (Hindu). I wouldn’t exactly call them friends, but I hang out with them sometimes.

The other day, while we were walking past a group of teenage Muslim boys, one of them casually said something along the lines of “they should just come under a train and die,” just because they were Muslim. I was honestly shocked. Like, how do you even say something like that so casually?

For context, I’m an atheist. I don’t care what someone’s religion is I wouldn’t want anyone to die because of it. But at that moment, I just didn’t know how to react. I was so surprised that I didn’t say anything, and now I feel like I should have. Even with comments like there are only Muslim territories, Hindus are never terrorist.

Have you ever been in a situation like this? How do you stand up to these things without making it worse? Aggressive people that won’t let you talk.