Welcome to Hotel del Luna - S1-E1
Stupidity: The Mayor realises that Man-wol has approached him and taken out her rifle to shoot him with. Yet during the entire time she takes to aim the rifle at him and fire, the Mayor makes no attempt to flee the stage for his own protection. (00:38:15)
Worlds Apart - S1-E2
Stupidity: The bad guy kills the deputy in the swamp, then later sees a little girl who witnesses the killing run away. He then searches the boat for a weapon and runs off after her after he finds a machete, without even considering the officer's gun still in its holster. Abby proceeds to make the exact same mistake later when she finds the dead officer (meaning there's danger nearby) and hears the girl screaming and runs in the direction of the screaming without taking the gun to protect herself.
Stupidity: The Resistance is a rescue team that helps the various protagonists escape schools. They do this by leaving intricate hints that lead to a detour to the school alarm instead of going straight there, setting off the alarm and rescuing the protagonists.