How to bevel a misbehaving corner? I want to add a simple rounded corner to this mesh, so I selected the corner and used ctrl + B to bevel it, but it bevels really strangely, it is very deformed.

Any idea what is wrong with it?

Blend file: https://files.fm/u/c5gd2hhc

Thanks
Your mesh topology is not good. You have inside faces (look into your mesh) – delete these.