1) A contemptible person of low intelligence.
2) A term of endearment for a person who has just done you wrong.
3) Relating a contemptible person to a sexual device in such a way as to equate such low intelligence with an inanimate object of gratification (i.e. a head with no brains).
"Oh you fucknob! You just ran into my car!"
"That Frank... he's one colossal fucknob!"
person(s) of extremely low intelligence who need to go fuck a knob.
"fuck you fucknob"