Originally an (shortened) insult to newcomers in forums or internet games e.g. counter strike, the word has been stolen and is currently being used as an insult with a different meaning. It is used in certain places to describe someone who is slightly - ahem - slow and ditsy. Basically it is used to insult a pesron who makes a stupid comment or somebody who makes many stupid comments.
"the tibula bone exists!" "no it doesn't you noob"