Mr. Monk and the Astronaut - S4-E14
Stupidity: Steve Wagner is shown expertly constructing an elaborate hanging machine, but he adds a superfluous complication by having it triggered by a garage door remote control that he posts to the address in question. Anything could (and does) go wrong! Why doesn't he simply have it triggered by a bog standard timing device that you can buy in a hardware store for a tenner? I am not sure I'd trust him with my space shuttle.
Mr. Monk and the Airplane - S1-E13
Stupidity: When the pilot asks Monk for some ID, who cannot provide it, and the flight attendant exposes Monk as the passenger that is causing her a lot of trouble, normally Sharona would step in in these type of situations to convince whoever with her voice of reason that Monk is indeed a famous detective and sought after consultant for the SFPD. Her silence in this situation and later when the flight attendant confiscates the lighter and takes the glass with the evidence residue is incredibly out of character. (00:30:40 - 00:32:30)
Mr. Monk and the Big Game - S5-E3
Stupidity: It makes no sense for the murdered coach's brother to stick around since they were getting close to him much less attend the game.
Mr. Monk Gets a New Shrink - S5-E7
Stupidity: Merrigan should've removed the heroin from the statues once he got them, thus the whole murder of the cleaning lady and discovery of his drug dealings might not have been discovered.
Mr. Monk Can't See a Thing - S5-E4
Stupidity: In the beginning, Natalie walks into the firehouse, sees two people hurt, and instead of calling 911 EMS, she calls the captain, delaying the EMS services.
Mr. Monk and the Astronaut - S4-E14
Stupidity: For being a supposedly clever guy, the astronaut doesn't think to wear gloves as he's fixing that garage door opener as part of his death device as a precaution.
Stupidity: It makes no sense why the staff or the guests would serve the wine to Natalie from where the dead body was being stored. The guests and staff go about cleaning up after he died to avoid any trace of him ever coming to the winery including putting his body in a large wine crate. Yet Natalie makes the discovery that the weird smell (of aftershave) from the wine which leads to the police discovering the body. There is no reason to serve her that wine. It was a vineyard after all - they had plenty of wine and as the staff was in on it, they could have made that crate inaccessible to serve. (00:18:35 - 00:40:04)
Suggested correction: The guests and staff involved had nothing to do with which wine was being served. Sylvia was just a hostesses and Ricardo was just a waiter. They happened to dump the body in a cask of the new wine which was being taste tested. The wine expert, bartender, and other waiters weren't involved and didn't know there was a dead body in the cask.
Mr. Monk and the Wrong Man - S6-E8
Stupidity: Instead of Monk pounding on the church's inner glass door for someone to let him in, he could have simply used the door handle on the outside which is the same as on the inside. (00:27:30)