Lot of us have students who are really angry. These are teenagers. I was a really angry teenager, outraged at the many injustices I felt I faced in the world. Nothing is fair when you're at the centre of your own world. (I'm still pretty angry, but my focus has shifted to injustices around the globe instead.) Adolescence is a necessary time of self-obsession as people figure out their place in this life, and that can heighten every possible sleight against them, provoking an attitude of quick-tempered defensiveness. But the vast majority are completely harmless.
Lots of us have students who let slip some racist or sexist or bigoted comments in class, and we shut that down but then linger over the comment a bit later, mentally reviewing it and filing it away, and maybe mentioning it to a few colleagues looking for a pattern. But the vast majority are completely harmless.
And lots of us have students with a mean streak: students who are trying out their power, looking out for the boundaries that might be able to reign them in. If they get away with too much, they sometimes keep pushing until a consequence helps them turn a corner. We know it's important to stop cruelty in its tracks, but we can't catch everything. But the vast majority would never consider harm at this level of violence.
But I'm left wondering about all the signs we're told to monitor. Is it remotely useful to psychologically profile students?