What irritates me is people who provide information with absolute confidence when they don't know what the hell they're talking about, and they know they don't know it. I've worked with asshats like that before, and I don't know what their issue is. If somebody asks me something, I'll provide the information to the best of my ability, and the accuracy approximately weighted so they can use their own judgment. That's not to say I give infallible advice, but I try to be accurate. The other people give the impression of knowing when they're clueless, and that's how fuckups happen.