The "Nut Job" has nothing to do with Sexuality. It is completely and utterly the term used to describe a Maniac, Just like a Nut Case.
In other words, it is an old man or stalker that has lost his mind; Or just a Hyperactive person that is all over the place and always looking for fun
(I don't always use the term do this example is going to be crappy)
DesertedChrome: "Yeah, I heard about him. He got arrested for multiple charges. He's a Nut Job"
Yah she sucked on his balls so well!