Star Trek the Next Generation and Deep Space Nine both ended up being much much better than what they were when they started, so maybe that accounts for the dislike some people have. I know I quit Next Generation after about two episodes and had to be talked into watching it again years later and was really surprised. I do still harbour a grudge against Deep Space Nine though, as the producers stole the thing from the pitch for Babylon Five. They rejected B5, then rushed into production with a Star Trek version they could own and control and got it out first, damaging Babylon Five, which was a classic show! DS9 itself was still good if I can get past that. I suppose now there are two rather than one.
That other Star Trek with Columbo's wife in it was also awful to start with but got way better.
Totally agree on Friends and Seinfeld. I actually liked Friends when it started but then it was just the same jokes over and over so I gave up by the end of season 1. Then it kept going and going and going and going and actually getting worse. Now I can't believe I ever liked it and even the song annoys me.
Some people say that Seinfeld was groundbreaking but hasn't aged well, so that it's not funny anymore. I never ever thought it was funny! Has anyone else ever tried watching clips from it with the laugh track removed? It's deeply odd and uncomfortable.
Other things:
The Big Bang Theory! I'd rather watch an episode each of Friends and Seinfeld than that one!
The X Factor.