Noob

Not to be mistaken with a newb;

"A noob (also spelled n00b) is a player considered to be "the annoying one". These people have the main purpose of aggravating people for their own amusement. A noob is considered to be the worse name to be called in Combat Arms. The word "noob" actually means "the new guy," but it is also used to make fun of someone who is being unnecessarily ignorant or annoying. Actual noobs call other players noobs mainly because they are very angered from getting killed a lot." ~Dallasc779

"Newbie (also said as nooby or newby) is a slang term for a newcomer to online gaming or an Internet activity. It can also be used for any other activity in whose context a somewhat clueless newcomer could exist. It can have derogatory connotations, but is also often used for descriptive purposes only, without a value judgment." ~Wikipedia

History
The word newbie is a variant of new boy and comes from British public school and military slang. Before it entered popular discourse by way of the Internet, the term "newbie" was used among U.S. troops in the Nam' War as a slang term for a new man in a unit or squad.

The earliest reports of the word Noob being used was on the USENET newsgroup talk.bizarre, and was first seen circa 1981.

The Insult
Whilst it's common these days to be proclaimed a Noob whenever you do something stupid or mistake a team mate for gun fodder, it's relatively a tame insult. The words may have been offensive; but due to it's over use it has been nulled. Not many will take offense to it, granted you haven't been 'Trolling' them.

Tactics
After a noob has figured out the basic controls, he may try blindly shooting, sprinting around trying to find glitches, crouching repeatedly on the bodies of dead players, or using noobnades. This involves lobbing a M67 (Frag Grenade) at the opposing base or random direction, occasionally resulting in a kill. A noob also only kills weaker people and usually joins the stronger team.

Difference Between 'Noob' & 'Newb'
Newb - Is usually willing to Learn the game and kindly take tips from other players, generaly innocent, but often insulted for their tactics, thus their willingness to learn. They are capable of getting better.

Noob - Usually Arrogant, Rude, Unwilling to learn, usualy thinking their the best at the game/Superior, ignoring the situation they are in. The words Lazy, Annoying, Arrogant, Little Kid, Spray & Pray, and rude can all be associated with a noob. They usually become worst and worst in playing.