Note: the fact that a syndrome can be applied to a sitcom or its episodes doesn’t necessarily mean that it was a bad show.
Some examples to show what I’m talking about appear below. Feel free either to add new syndromes or to give examples of some of the syndromes already mentioned.
MY FAVORITE EPISODE syndrome: occurs when a sitcom is so formulaic you can state ‘my favorite episode was where ________’ and describe half the episodes of the series. Examples: “My favorite episode of Gilligan’s Island was when they almost got rescued and Gilligan screwed it up”, or “My favorite episode of Three’s Company was when the landlord made a gay joke about Jack and there was a sexual misunderstanding that led to chaos”.
START ANY MONDAY syndrome: similar to the above this occurs when a series lasts for several seasons but is so static in terms of cast and plots that episodes from the 5th season, 2nd season and 7th season could be watched back to back and you’d have no idea which came first. Examples include The Jeffersons (any given episode will have George calling Willis a honkey, Florence making a wisecrack to George, and no change in dynamic from any other season; were it not for the comings and goings of Lionel and his family there’d be essentially nothing to date any episode plotwise).
BUT THAT’S NOT WHAT YOU SAID LAST WEEK syndrome: when a plot development completely contradicts what’s been said in an earlier episode and there is never a resolution. An example is Archie Bunker’s family: in an earlier episode it’s said that he has a sister Alma and a brother Fred and that his father recently came to visit. In later episodes he’s an only child and his father died many years before. In yet later episodes he has a brother Fred again, but no mention is made of Alma.
RASPUTIN SYNDROME: named for a SDMB thread that gives umpteen examples, it’s the syndrome when a show just will not die long after it’s “jumped the shark” and qualitatively gone to sing with the Choir Invisible.
THAT’S FUNNY, THEY NEVER MENTIONED THAT BEFORE syndrome: occurs when a plot is built around a major facet of a sitcom character that has never been mentioned before. Examples include: a two part episode of The Jeffersons revolved on George’s passion for and encyclopedic knowledge of murder-mystery novels, something that had never before been mentioned; episodes of ALICE and SANFORD AND SON both dealt with a main character (Vera and Fred respectively) battling to quit a long habit of heavy smoking even though they’d never been seen smoking on the show before.
FLOWERS FOR ALGERNON syndrome: occurs when a character has major fluctuations in IQ throughout the series. Examples include Kelly Bundy (who in early episodes is slutty and bitchy but not stupid) becoming dummer than moss by the last 21 seasons, or Screech who goes from weird with a major slant towards stupid to super intelligent computer geek in some episodes.
JUST HOW MUCH RENT CONTROL DO YOU HAVE? Syndrome- perhaps the most ubiquitous, it occurs when characters live in absurdly huge or lavish apartments for their income. (There are too many that come to mind to name them, but one of the first times I noticed it was on the old primetime Spelling Soap Hotel, in which a desk clerk {desk clerks make little more than minimum wage} had a very nice modern high rise apartment that she paid for on her hourly wage.
WHO’S MINDING THE STORE? syndrome- occurs when characters just suddenly and non-chalantly leave work. Again, the same desk clerk on Hotel (Connie Selleca?) would walk away from the Front Desk even when she was the only person on duty. Other offendees: Designing Women, who would close up shop during the day to run see Berniece and for that matter never seemed to be working anyway.
Please add some more syndromes or examples.