Free Family Portrait Studio - S8-E24
Stupidity: Dwight is seen walking out of the bathroom with the diaper in the direction of the main part of the office in which Angela sits. If he was to try to stay hidden (which was obviously the whole point), he would have gone through the exit of the annex, waited until she was distracted/or hide it for later and Angela never would have seen. This was done because the plot required for Angela to notice but Dwight could have easily kept it hidden. (00:10:40)
The Power of the Doctor - S13-E9
Stupidity: While on the Cyber planet in 1916, the Doctor receives a call from Kate Stewart telling her to come to Unit HQ in 2022 immediately, prompting her to then reluctantly ditch all her problems she's currently dealing with, to go to Unit. The TARDIS literally has all the time in the universe, so even if she waited a really long time, the problems in 2022 would still be there, so there was no need for her to change plans so abruptly.
The Best Burger in New York - S4-E2
Stupidity: Marshall says "The tiniest little burger joint you ever saw, tucked between a taxidermist and a triple-X bookstore."They could have just search all the taxidermists and triple-x bookstores and look for which ones are located together.
Stupidity: When they are conferring before surgery everyone is keeping scrub except for Avery who has his arms crossed. Shortly afterwards you can see him look around at all his co-stars, realise he screwed up and try to casually raise his arms. (00:15:00)