Stupidity: Damon and Stefan are trying to get Elena's humanity back - they could have just asked Rebekkah or Klaus or Elijah to compel her to turn it on.
Stupidity: When Castle and Beckett discuss the trap LokSat set for them at the dead drop and any forthcoming retribution, Beckett comments that her dad should be relatively safe from reprisal because he's on business out of town. Someone as smart as Beckett would never make such brain-deadly dumb assumption; considering how powerful and how dangerous he's supposed to be, especially with the resources of the CIA at his disposal, LokSat surely would have no trouble finding and getting to, and certainly no qualms about eliminating, Beckett's dad if it stopped her in her pursuit of him.
Stupidity: For their set list at regionals, Schue chooses a medley of Journey hits. Since his kids are considered the competition's underdogs, and it was pointed out to him in the previous episode that Vocal Adrenaline's weakness is funk music, he should have used that info to New Directions' advantage.