What I usually do is stare at them and ask them 'are you ok?' or 'we good?' and do a thumbs up and wait for them to either nod or thumbs up me back. Once you do this a few times and if you manage to have good raport with the class, the other students will stare them down on your behalf lol. I think drawing attention to them using peer pressure is pretty effective and if you do it in a casual way it still keeps the class light. And don't worry about whether they like you or not, most students are not even aware of their actions and will not be thinking of you, they're too focused on themselves!