The word came from an online article about a farmer that was accused of molesting a pony. The pony appeared disturbed, and there was the farmer's wallet on the ground. (Legit story)
The "pony" part of the word come from the accusation of a creep stalking another innocent bystander. The creep is called the "farmer."
The "nub" (not pronouced n00b) was a accidental misspelling of n00b, but was accepted as nub.
Putting the two words together makes "ponynub." This tends to refer to innocent, yet lame people.
Yo, hipster. Why are you a ponynub?
Dude, I don't know... (sad face).