n00b13
Someone who thinks they're the best at something but can't even complete the first level. They're like a kid who thinks they can win the race but trips over a pebble.
"You're a n00b13. You can't even beat me in 2 minutes."
In chat: "This guy is a n00b13. He quit after 3 seconds."
DM: "You're a n00b13. You didn't even know how to use a sword."