Well... to tell you the truth, I've no idea how my username came to existence. I was trying to think up a quick username to re-register on GameFAQs and I instantaneously thought of snowboarding... someone crashing down a cliff and off the border (of the cliff). Then I just converted "the" to "da" to hide the fact it took me ten seconds to come up with the name. Yeah I know, you want to kill me now. :p
ODB is the abbreviation. Back on GameFAQs on the prerelease NFS Most Wanted (I believe) boards some guy decided he needn't bother to type down my full username and went for the initials. Lo and behold, every single creature I know over a bunch of wires and a screen now knows me by nothing but the initials. Only a long while later on I realised those same initials also denote the unthinkable...
Border is another abbreviation, but is much less common.
Odb8492, my TDU ingame username, is the aforementioned abbreviation plus 8492, the designation of your antagonist squadron in Ace Combat 5, specifically from one of the toughest missions in Ace Combat history, "8492".
Then there's X-49 or X49, which is essentially the designation of a prototype aircraft from the Ace Combat series (specifically Ace Combat 3). No, not the US' sorry excuse for a high-tech chopper, but the boomerang shaped fictional hypersonic plane with lasers mounted on its forehead.
Oh, and sorry for bumping an old thread, felt like ranting a bit. ;)