I have two episodes that I just hate to watch: Ted and Normal Again.
An abusive stepfather just stalls the rest of the series arcs and I don't see control freaks like him as entertainment in any sense. The story of him being a robot who has killed before and has relationships stuck in the 1950's is a plausible plot, but the malice towards Buffy is repellent to watch.
Normal again just destroys the entire Buffyverse for me. Yes, the story says Buffy is poisoned by a demon and this is what causes the dissociative state, but I was left wondering whether I was a fool for spending time watching something that was obviously the product of insanity.