Have you ever tried to kill your teacher or even had the thought of doing it? (Don't do it...but you know what I mean, hating your teachers sometimes).
Ansatsu Kyoushitsu or "Assassination Class" is about students trying to kill their teacher (an octopus mutant alien) before it destroys the world.
Another hidden gem for those looking for a different style of school anime with lots of comedy, action and thrill. I believe it is worth your time as it has a decent story with charming characters (especially the teacher), but the comedy element is what makes this anime a hidden gem.