People that absolutely insist upon everybody converting over to their o/s. Whether it is Mac or PC or Linux, Solaris, BSD, OS/360 -- it doesn't matter. Just don't try to be one of those religious freaks that go around converting others.
Overclocking fanbois, we don't care about the extraordinarily heroic lengths and excessive money-spending you do to get an extra 8Mhz from a +2Ghz i7 .. we really don't.
Even worse are the tough guys putting those sissy lights in their computer. Do you spend all your time looking into the box to see pretty lights? I bet it's because your $200.00 water-cooler hasn't managed to stabilize your system yet and enough to have a usable system.
IT guys that think they are master of their little domain holed-up-in-the-basement-of-wherever-they-work, that sort of attitude. Nope, you can be replaced at the whim of HR. Even worse is when they think they are gods everytime they fix something.
And more worse is asking one of them to show you how they did what they just did. They sit there all self-inflated and gloating. Like they know everything. Best thing is not to feed them anymore, and then fake like you understand. Most commonly this happens with the fat ones, especially if they have a beard. They are also loud and boisterous.