A stage in life in which a normal person undergoes the initial changes that will eventually lead to nubhood or their coming into nubhood. Similar to Puberty only it tends to work in reverse, they become weaker, less coordinated and ultimately suck at life, thus they become a nub.
He was such a cool guy, athletic and smart, then all of a sudden he lost 30 pounds and started sucking at Halo... he must be going through Nuberty or something.