In my several months of actually being on Facebook and participating to a certain degree, I seem to have figured out how to avoid most of the things that would annoy me the most. The one thing I can't get away from is stupid -- people who are just totally unfocused regardless of the topic of discussion. Too many are there to mindlessly gab, and actually have nothing of value to add to a conversation about a specific thing. Or they are interested and excited to contribute, but they're too lazy to read anything that's already been posted, so you'll see the same "answer" or "observation" being given over and over, with greater and lesser degrees of comprehension and accuracy. And the ease with which the digressions flow and get taken up by the sheep others is mind boggling.
I'm sure this all sounds very judgmental. I guess since I'm primarily there to take part in certain groups, for specific reasons, and not just to hear myself chatter, this is all the more obvious to me. And some groups are more disciplined than others. It's the ones that appeal to a broader audience that can be the most frustrating at times.