The big one for me is "tweek vs craig"; it feels like two different episodes crammed into one. it has 3 plots; the fight, mr. adler, and kenny in home-ec, but they barely interact with eachother aside from in a very contrived way at the end, and they're not thematically related at all either. but the worst thing about this episode is just all the wasted potential; not only could there have been so many more scenes of craig and tweek training, getting them to train, interactions with their families, etc. but there's also so much they could have done with a shop class episode, or a shop vs home-ec episode. yet in the episode we got the shop class was only used as way to shoehorn mr. adler in. this needed to be 2 episodes.
What are some other examples of wasted potential?