AS noob is a person that purposfuly degrades and/or ruins the experience of a game and/or life in general for other people. This can happen through lack of common sense, name calling, betrayal, hacking, breaking rules, encouraging others to break rules or just all around being not a nice person.
Do NOT, DO NOT confuse this with newb, someone that is new. Sometimes noobs can be newbs, sometimes someone can be a newb but not a noob and extreme cases a noob can be some1 that is not a newb.
As this pretains to gaming: Using cheat codes to beat a game the first time. That makes you a noob.
As it pretains to life in general: Flushing the toilet while someone is taking a shower is noobish