Stupidity: If Jordan was inside the cake and the cake was right there in the room when the takeover began how did the bad guys forget she was still inside?
Stupidity: When Marlene deduces "Peyton" as being Dr. Mott's widow, she drives to the house to warn Claire. When she arrives, she foolishly decides to confront Mrs. Mott with this knowledge right to her face and demands to know where Claire is... which ends up with her being killed in Claire's place. Instead, she simply should have waited or looked for Claire, rather than confronting "Peyton."
Stupidity: It's very idiotic that Michael and Karen kept the same security password, even after being harassed and not feeling comfortable with Pete being around them any longer. There's no way the pyramid password should have been kept the same, with Pete being able to enter their home, plant drugs, and frame Michael. Changing your security password, the same password that the lunatic cop once knew, would be the first thing to do after his psycho behavior starts.