https://blog.clearbit.com/managers-handbook-tldr/
Setting boundaries People will push and prod to discover your boundaries. Occasionally someone will push too far. When they do, you have to show a rough edge or you’ll lose authority with your team. A firm “That’s not ok here” or “I’m not OK with that” is usually enough. If you have to firmly say “I’m not ok with that” too many times to the same person, it’s your job to fire them. Don’t laugh things off if you don’t feel like laughing them off. Have the courage to show your true emotions.