It's good when one can recognize they're doing it at all. The terminal a-- hole is the one who really believes they know it all.
I once saw a bumper sticker that said "Hire a teenager while they still know everything." I'm sure we all know someone who peaked in high school. They are the people who fit into this insufferable category.
When a person feels as though they need to prove themselves all the time, they are in real danger of being one of these types. It is much better, when asked a question you cannot answer, to simply say so. I don't know, but I'll find out for you, is a viable answer. A truly wise individual, is one who knows enough to know they know nothing.
Today I am quite happy and relieved to know I don't know much. For those of you who know me personally, please feel free to call bull shit on my bull shit. I'd rather be embarrassed for a moment than insufferable all the time.