To unlock the Bully of Bullies trophy in Little Nightmares 2 you'll need to crush the bullies with the bookshelf when they chase you after being spotted in the area where you need to avoid the teachers vision. You're supposed to sneak through in order to grab the key on top of the shelf. It's easy enough to die getting this trophy and then reload the checkpoint to attempt the successful strategy. Here is my own video guide that shows how to get the Bully of Bullies trophy along with all of the other collectibles / trophies Little Nightmares has to offer. The Bully of Bullies guide appears at around the 8:52 mark during the video.