Just a quick rant, for a change.
While Twitter is mostly OK (I don't use it as much as Facebook for connecting with IRL friends, but I've got a handful of online acquaintances I mostly connect with on Twitter, plus celebrities I follow), there are a few things about it that sometimes drive me nuts. These are (mostly) related to the users more than the technology, though (unlike on Facebook, where the occasional buggy behaviour is usually the worst annoyance).
Firstly, there's the 'replace X with Y' hashtag memes, where X is usually something like songs by a certain artist or movie titles, and Y is some random, silly word. The problem is that the wording of the hashtag is, semantically, completely wrong. If you replace X with Y, it becomes Y, and nothing but Y, and not some (supposedly) funny hybrid of the two! Yet these hashtags pop up in the trending topics often enough to drive me absolutely crazy. Seriously, language matters, people!
Slightly less annoying, perhaps, but still annoying, are the frequently trending 'national something or other day' memes. Seriously, people. Which nation? Why only them? Why am I left out? News flash: the net is global, folks!
Lastly, the one major technical flaw in Twitter is the fact that they allow animated profile images. This is something I really hate. Any unnecessary movement on a web page is an instant turn-off for me.
None of the people I follow participate (actively, at least) in these faux pas, I'm happy to say.