Reika Hayami and the Uninvited Guest - S1-E5
Stupidity: The plot hinges on the fact that the culprit switched clothes with the guy in the bathroom. It would be unfair to say that they do not address the issue, since both the shoes and the belt buckle are mentioned. However, this can work just in a cartoon, since he could wear without any issue and looking absolutely dapper the jacket and shirt of an obese guy. Anyone trying that in reality wouldn't just have to tighten the belt.
Reika Hayami and the Uninvited Guest - S1-E5
Stupidity: A rather unnecessary part of the plot focuses on the convict trying to learn Reika's last name by ordering something on her behalf to read the name on the bill. That's absurd; he couldn't possibly know if the bill would just have the number of the cabin on it instead, or the production company's, and quite frankly for such a VIP (the cruise itself was a one-evening trip around the bay just so fans could spend time with their idol Reika, and he knew that) the ship wouldn't even charge anything for a drink brought to her room.