Big-Lipped Alligator Moment: A lot of Eli's cameos are completely self-contained gags totally separate to the rest of the episode and very different in tone. This doesn't stop them being hilarious.
Wally Batty's brief appearance in "Getting Sam Home", stumbling drunkenly to his front door, only to be discovered and accosted by his wife, Nora, did not need to be in the movie at all. It seems to have been included (thankfully) just so that Wally would appear in the movie.
Seasonal Rot: For a 37 year long run some seasons are bound to be better than others. Though there is a general consensus that things were never quite the same after Compo passed away.
Squick: In-universe, Clegg is cripplingly susceptible to it, particularly anything involving women and sex. He completely falls apart any time a woman, especially Marina, comes on to him.
Unpopular Popular Character: Foggy. No one seems all that fond of him in-universe, but he is considered the most popular "third man" character, and his time as the de facto leader is considered by some to be the series' Golden Age.