The least realistic part of Harry Potter is the school teaching students how to fight boggarts with a life demonstration.

Not because they didn't need the lesson, but because, SERIOUSLY, half of the class would commit suicide the next few weeks.

Just imagine the class bully learning that he is in fact THE FINAL FEAR of half of the class, and the onther half can be ruined with just a bit of imagination. (for instance, 10 min of catching spiders.)