I'm not sure if you mean "Which episodes do you find bad" or "Which episodes have controversial matters" but as for my finding what I thought was bad:
Foster's "Cheese A Go-Go".
It had the usual great writing of Foster's, ie: 1. Taking one idea and stretching it into endless possibilites 2. Making things as hetic as possible to drag and keep you interested 3. Interactions between all/most of the characters, etc, and yet, I had not been so bored with an episode of Foster's.
Because despite them doing all the things you would see in something like "Bus the Two of Us", each character had only one gag to stick to and said it throughout the episode making it boring and tiresome. You barely got to get sucked into the story because it felt like it they had a huge chunk of the beginning missing and just randomly started at the middle, not letting you know what's going on until half the episode has aired to at which point, you don't really care that much anymore.
And rather than having all the characters' plots or stories submerging into one, they all seemed to just go into their own plot in which all of them didn't have an ending.