We are a fairly large group of friends from Bergen, Norway and this expression was born when a friend of our started with some strange behaviour. When we were hanging out he suddenly just left and did not return for several hours. The strange thing about it was that he acted like nothing had happen. This happened from time to time for a few years, and to this day we still have no clue what he did or where he was. From that day the expression has grown from our little click to become a more or less common word in our city amoung the youth.
1) If you cant get hold of someone for some time he has "done a Geddi"
2) If you have a conversation with someone on icq or MSN and they suddenly stop replying, they have "done a Geddi" i.e. "He did a geddi on me"