Doon is an abbreviation of the term 'What are you doing?', which eventually formed 'What you doon?', then to 'Doon!'. Coined by the famous Hanc.
It can mean anything you want it to, such as a greeting or added in general conversation.
It has also aided in the creation of the language 'Doonish'.
Chris - doon!
Barry - doondaloon.
Chris - did you go oon last noon?
Barry - yeah it was foon mentoon, this goon was all over my coo.... errr... cock
Chris - skoon
Seldom used to flag someone who is out to make drastic political changes. It may be used for one who's views favor radicalism or someone who wishes to be a revolutionary. Sometimes it is even used to pin someone as an anarchist.
Doon was given as the last name of a character from Hot Sleep, The Worthing Chronicle and The Worthing Saga, written by Orson Scott Card. The tale includes a man, named Abner Doon, who helps destroy man's civilized planet, Capitol, and has a new planet populated by humans with telepathic abilities, called Swipes.
Doon was an ancient Breton lai of a knight who strives to win the hand of a maiden.