1. One who mongs dongs.
2. A person who is known to be an annoyance to a particular group of friends, who secretly dislike said person.
3. Less used insult similiar to "dick-head."
DONGBONE is English slang for the penis / todger / pecker / one-eyed-trouser-snake / wee willy weiner. The name probably springs from the often discussed (and false) belief that the human member contains a bone which allows it to become errect.
MINGER: Wow, look at thatamazingly fit bird, I'm going to ask her to touch my dongbone!
AMAZINGLY FIT BIRD: I'd rather eat the scabs off a dead leper's back.
A portmanteau of "Do nothing, go nowhere"; in essence, it is a term for a person with no ambition, no drive, and no desire to make themselves a better person (by pursuing a better career, higher education, etc.)
It's nice to know that when I become a success several years from now, these dongons will still be working the samedead-end job.