Being an Admin myself I know how some noobs can be, but sometimes they don't know how annoying they can be. Most of the time I get asked the question, can I be OP? Well let me say that is the most stupidest question you could ask. Why people try I have NO idea. They are not going to get it and usually it leads to a ban.
Normally, I see the Welcome [username] as a good thing and it is, until they say something stupid. Something like how do you get out of spawn

When it is right in front of their faces as soon as they log in.

Other than the stupid question people, there is only one other kind of noob that I hate. Griefers.
I set up "baithouses" designed to catch griefers. They are usually made of wood and have a farm. Then when I catch them, they actually try to argue and say they didn't do anything. Argh that just ticks me off. Oh and another thing, when people pour lava in houses that is even worse than them arguing. The mess that I have to clean up because they were being stupid ASDF.
Anyway I think all us Admins and Mods etc can agree that if Noobs would just use common sense we would all be a lot happier. A lot happier.