Sheila's always had it in for know-it-alls. I never thought about them much as a type until she told me about them. I have it in for know-it-alls too.
They're young, in their teens, 20s, or 30s. They answer every question. They volunteer answers even for questions they haven't been asked. They always act like they know more than everybody else. They never ask any questions -- unless it's a made-up question to prove how deep and original a thinker they are. Or unless the question itself is an attack of some kind, and they don't really care about the answer.
Difficult, shaded moral and ethical questions are always very clear to the know-it-all. They tend to be true believers in something. Lines are always very clear and hard, there's no room for the actual complex anarchy of life in their thinking.
They're intolerant for sure, lacking in empathy, and tend towards cynicism, reserving praise only for the objects of their faith.
Know-it-alls are almost always men, but not always; even if they're women they tend to be condescending to women, who they apparently think are good creatures who just don't know things.