Having competed for four years as an NCAA cross country/track athlete, I can attest that the sport is full of assnozzles.
That said, I find that people who are actually serious about the sport/good runners are pretty tolerable. The annoying ones who blow up Facebook with ridiculous crap are the girls who spend 30 minutes before every run deciding which Lululemon top to wear or the guys who extoll the virtues of Vibram 5 Fingers and post some sort of Nike+ update after every single run.
I have a buddy who was an All-American runner in college and ran professionally for 2.5 years post-college. He passed on this bit of wisdom that perfectly encapsulates running, "It's faggy, and it ain't worth it."
Edit: basically what Vicks Kennel Club said
This post was edited on 11/15 at 2:27 pm