I honestly feel that what we consider to be "noobs" shouldn't always be fit into that crowd just because they resemble one, some of those "noobs" are probably a lot more interesting than the older well-known denizens of wherever they thrive.
I also usually don't use the word "noob" very often, this is probably the most amount of the slang "noob" I've ever put into a sentence. If I were to consider what a "noob" was however, it would be someone who constantly belittles everyone, regarding they have no right too, anyone who goes terribly off topic, and anyone who messes up anything well built. These are only just a certain amount of reasons I can think up, why anyone should be considered a "noob".
I quote the slang term "noob", because I hate the slang term strongly. It's just a shortening of the slang term newbie, which I consider a corruption of the word newborn.