I think a lot of the attitude starts out as just not knowing what to do, and then getting angry at the source of confusion, more than the "I shoudln't have to slow down for three seconds!"

But... lots of them sincerely believe we should keep our little toys on the sidewalk. I gave the boy who pulled his big pickup out in front of me on our city street a horn blast, and he stopped and rolled down his window to inform me that he had seen me... and "You had plenty of time!" Of course, I had the right of way -- having time to stop without hitting him wasn't the question... but he went on to inform me (while driving, now) that I should be in the bike lanes -- that aren't there. Then we *got* to bike lanes and he pointed to them and told me that's where I should be riding...