It's rude to pointlessly criticize someone on their job.
Alex has been watching Theresa work, every day, as a colleague, and he notices things that she is doing wrong.
Alex wants to advise Theresa on how to improve her work performance.
Alex mentions to Theresa that he found a better way to work, and he shows her what he's been doing.
Alex lists all of the things that he has noticed that Theresa is doing wrong, and he tells her she needs to do a better job.
Theresa is willing to listen to his idea about a better way to do their job.
Theresa is defensive and offended by all of the criticism, and she ignores Alex's unsolicited list.