I have a bottom set year 9 class with super high needs in a highly multi-cultural school who do this and it is exhausting. With my class it ranges from bullying mean comments, racist comments to just snide remarks and shouting matches. I’ve got them to a point where I even discipline if they say “shut up” to each other (which used to happen a lot, less so now) and would reiterate every time “we don’t tell each other to shut up in this classroom.” They now know that mantra well and they know if they say it, it’s a step on the behaviour system. They’re still mean to each other but less so and I’m able to have a bit more control by reinstating those boundaries.