Mr. Monk and the Naked Man - S6-E3
Character mistake: SPOILER. Arlene Boras murders Vicki Deline in order to stop her telling Peter Magneri that he has an aortic aneurysm. Boras wants Magneri dead to clean up by short selling the stock in his company. Boras is a medical professional, and she would know that an aneurysm can burst if the patient is under stress or is shocked in some way. Allowing Deline to tell Magneri that he is in danger of dropping dead on the spot would kill him, which is exactly what she wants.
Mr. Monk and the Naked Man - S6-E3
Character mistake: SPOILER ALERT Monk accuses Arlene Boras of swapping Peter Magneri's X-rays in order to hide the fact that he has a potentially lethal aortic aneurysm. We see Magneri being examined and we see Boras handling his records, and they are not X-rays. Magneri was examined in an MRI scanner and Boras swaps the MRI scans - not X-rays.
Mr. Monk and the Three Julies - S6-E13
Character mistake: Julie has just passed her driver's test. At the end, she drives up with two teenage friends in the car and offers the stranded Captain Stottlemeyer a ride. Instead of simply accepting, by-the-book cop Stottlemeyer would be lecturing her. California law prohibits new teenage drivers from having other teens in the car. (00:40:15)
Mr. Monk and the Three Julies - S6-E13
Character mistake: When Monk's examining the second dead Julie, notice that Randy touches the body to point out a bruise. Surely real life cops would be wearing gloves so as not to contaminate part of the crime scene.
Mr. Monk Paints His Masterpiece - S6-E14
Character mistake: While the concept of the knife height and stab wound is OK, the way Monk measures the height of the knife is way off. He says it's 48", which is 4 record lengths, but he doesn't put the bottom of the record where the top previously was, sometimes he only moves it half way up. Then the top of the record is above the knife, so it couldn't be 48" even if it was done right. As particular and accurate as Monk is, he wouldn't make this mistake.
Answer: The two men are trying to work out a secret deal between them without involving the union, which means the workers' interests aren't being represented and defeats the whole purpose of a union. The mayor would lose labor's support and Cusack's union troubles would just be starting.
Captain Defenestrator