To quote George Carlin, "I don't have pet peeves -- I have psychotic f**king hatreds".
Man, there's so many. Traffic-related ones alone could produce a 50 page thread. I detest people who hold up the flow of traffic in the fast lane, especially when lanes to the right are available. And what about people who get in line at the grocery store, and then meander off to browse for other items, as if the whole line is obligated to respect their use of the shopping cart as a placeholder.