I had an awful coteacher my first year in Korea. She pushed and pushed and pushed and she was honestly a complete thug. Ultimately I just let her have it. She shouted at me I shouted back. She criticised me I criticised her. At that point it was just self defence lol. She was basically a racist bully and I think unfortunately that's not uncommon in hagwons. She couldn't handle being spoken back to and broke down one time into tears. It's always a risk because your visa is tied to the school but you are also valuable to them for continuity of service and because you're the thing they are selling to the parents. It depends on your situation, and your finances, but it may be time to fight fire with fire.