Evil things coworkers have done?

I am writing a novel. What are some absolutely evil things a coworker has done to another teacher? Bonus if it is something that is Korea specific Just to get this started. Therebwas this guy that hit another teacher. When he was going to be reprimanded by the foreign teachers in the administration, he threatened to report the teachers doing private teaching. Some of those teachers had given him rides to the ski slopes.