Larb
One who is a Larb is a person incapable of accomplishing his/her goal due to the fact that they try too hard to impress and be good to the point where they do the exact opposite and fail completely at accomplishing their goal. Usually a Larb will insist that they excel at what they are trying to accomplish and will blame others for their mistakes or defeats.
Larb:YO WHY ARE YOU SO BAD LOG OFF NOW, YOU SUCK, YOU'RE MAKING ME LOSE

Player:That guy is such a Larb why is he on our team?