People (ok... guys) who turn into simpering idiots desperate to please when a (pretty) girl gives them some attention.
Guys who smirk at guys like that and make fun of them and pretend they're above it, then do the exact same thing.
Myself for being one of them
People who manipulate others into doing something for them, and then ignore them when they no longer have a use for that person (yes, most of my experience is women doing it to gullible men, but it's not only women that do it.)
Receiving the same joke via email from different people, when they get it they just forward it to "everyone".
Trying to help people with computer problems over the phone - "click on the start menu" "what's that?" ARGH!
People who, at a gathering, choose the worst and most horrific news stories, and try to talk about them in detail (my family is especially guilty of this... any family thing, and the latest rapes, murders, and crime sprees will be discussed in as much detail as possible, while referring to older cases of equal or more horror.)
People who ask a question they already know the answer to (or can find out themselves very easily) just to be saying something.