Its a regular topic but I missed it here ... so I made it ;)
What inspired you to come up with your username? A tragic back-story? A game? A favorite picture? Do tell!

As for me, I made it up because I wanted something unique, and I loved V for Vendetta and Voldemort from Harry Potter so I wanted something with a V.

I think my username says it all - Its my first name

Previously before I changed it I had it set the same as the first part of a few of my email addresses which is a combination of my first, middle and last names.

Mine is mostly my first name.

For the rest, many years ago I was in London and went to a night of mixed entertainment at some pub somewhere (I was not yet a live music person, so it was anomalous, and I don't remember much about it). There was some singing, and some light panto, and some stand-up, and one pair of guys did an improv bit which ended with them improvising a heroic poem, taking a name for the hero and a couple of items from the audience.

I was volunteered to be the hero, and so their saga ended (after dragons, maidens, wizards, etc.) with something like:

And so it is fitting the stories are told
Of the heroic adventures of Linus the Bold!

It's a particularly clever bit of improv, because it sounded incredibly impressive - it went on for several minutes, all in supposedly-spontaneous improvisational rhyme - but in fact all you have to do is memorize this long rhyming poem and then slot in the names and items supplied by the audience. Anyway, it makes a great user name.

Obnoxious_Asshole was too many characters.

Seriously, this:
http://www.dailymotion.com/video/xgx4tj_tiny-elvis_shortfilms

Parents have a painting of a vineyard, so I took the name of the grape in the painting as my own.

I've used the Undeadcow monkier for some time, in high school I really liked horror movies and I'm a vegetarian so I thought it was a nice play on both interests and found it funny to imply cows are eerie.

BillyMaysFan59 is my username because... well, I'm a fan of Billy Mays! That is that.

Also, 59 is in there because it's a random and odd number, and it has a nice ring to it.

It's my real first name, I just replaced the vowels with digits.

You two were a gang of rapists and you raped your rape buddy's sister? You sick bastards!

Now seriously, I have no idea what "RP" means, especially as a verb.

name of my character when I played AD&D back when I was 4

Well I got the name from POP (Prince of Persia) series. If you don't know Kaileena is the name of the princess of time in the game :)

It was on the wristband when I escaped the genetic experimentation laboritory.

Its an old defunct student number, which I despise :P I didn't much care at the time. I only created a gog account to get Age of Wonders and Disciples 2, but then I decided to stick around :)

I signed up on GOG as I read about the existence of Treasure Adventure and that it was for free on GOG.com upon signing up. So, I signed up using the first part of the game I wanted in the first place, got Treasure Adventure and then forgot about the account until the end of October 2013, when some games I wanted to get on retail anyways came on sale at a price I couldn't resist. And thus I got my username and remained in the site and got to know this great community ! :-)