This blog post by Scott Meyer (of Basic Instructions fame) outlines something I suffer from: The rage caused by other people's ignorance. The Da Vinci Code was a classic example of that. Regardless of the merits/demerits of the book/film/computer game, much of what was stated as 'fact' was just plain wrong. And stupidly so, in some cases.
Another thing which gets me all fist clenchy and muttery is when people start slagging off Star Wars, then let some reference slip which means they're thinking of Star Trek.
I also loathe people who think they're funny mocking Star Wars and pretend to be the first person ever to make the 'Pizza the Hutt' gag. It was in a Mel Brooks movie, for criminy's sake. That's how unoriginal you are.