1) You can call that as a "tease", but I wouldn't consider that as "flaming". Flaming is toward a person who you think that person is doing a wrong thing.
2)No, I wasn't being called noob when I was new to this site. Probably of a...well he was well known back then...I joined because of him (although he's gone now), and I made lots of friends from him, they are Missy, Tsuna, Aifa, etc. I met all the nicest people when I first joined. Plus, the members back then were pretty nice and modest. Unlike the noobs now calling others noobs when they've joined for 5+ years. But yes, I was called noob recently, just because of simple disagreement, I found it the funniest.
3) To me, the word "noob" represents a newbie of course, but the meaning behind this "slang"-like word is the same meaning of calling an Asian American "banana", which I've been called that a lot. It's just a word that is made up and being used often, but this word could be offensive to some sensitive people, some people wouldn't care, or even like it.
4) Barely, because what if that person can't take it?! Unless they are really stupid to the point that he/she doesn't even know what he/she is doing here, or posting an anime-related thread here saying that he/she didn't see that, that's when I call that person "noob" (without typing it out.) Or if that person gets mad at me and call me noob, I'd be like "excuse me, look who's the noob?!"