Stems from the word pro + noob = proob.
1. The state in which an individual feels he is an expert at a certain skill or craft, but in all reality he is inefficiant and lacking in any sort of skill.
2. A person who feels he is all knowing or knowledgable when it comes to video games, or a person who feels that he is the god of gaming info and eliteness yet the lack any history/origin of the game or gaming in general.
3. Someone who is unexcepting of a particular genre or artwork of a video game.
eg. A friend who plays warcraft 3 all the time yet when you ask. "Hey wanna play defense of the ages?" They respond with what the heck is that!
Or someone who sees a game that implements the use of experience, and says "Oh that game is copying WoW." Yet the game is 10 years before the release World of warcaft.
"Check out this new game I got its an rpg."
"Does it have multiplayer?"
"Um no its a single player rpg."
"What! this is garbage!"
"Because single player sucks."
"... your a proob."
"The graphics look like crap im not playing that!"
"What ever proob."