As a youngster a local elderly woman who lived in an utterly cool, dull black Victorian with heavy undergrowth and gigantic monkey-puzzle trees in front, was universally referred to as ‘Shagnasty the Witch.’ I had a moment of mental confusion when I found out you were male ;).
My handle, as noted before, has little to do with the rather lurid exploits of my namesake. Rather it relates to me being attracted to it as a mysterious and exotic-sounding name when I was young.
Mine’s another Discworld character. It seemed too presumptuous to call myself Granny Weatherwax, there was already a Nanny Ogg, and I’m too old to be any number of other females in the book. Mrs. Cake (a small medium) runs a boarding house for the undead and has a werewolf for a daughter. She is feared by priests and mailmen. A minor character but a fun one.
Mine’s based on the fact that I install satellite dishes for a living…
… oh, and I’m a guy.
S^G
Lets just say that gravity is a harsh reality after my studly Marine Corps years. 
Mine is the initial and last name of a real person; male, deceased and minorly notable. (I’m female, alive and completely obscure. Oh, btw, I’m not an economist either, og forbid.)
Why Thorstein Veblen? It was purely a whim. I read some of his stuff back in college and rather got a kick out of the old coot. First, he was a whackadoo eccentric in the tradition of Grand American Misfits. Second, his concepts seem so obvious now, i.e. “enough” is a useless economic construct for the simple reason so many people lack upper limits at all for ridiculous, mind-staggering wealth and stuff. Third, it always struck me as funny–still does–that it took a reclusive loon to point out salient features of robber barons, nouveau riche hustlers and the Gilded Age for economists.
Not a very good screen name, though, as it caused more confusion than it’s worth.
I lurked for a while before joining, and when I signed up, I wanted a name that would be convenient for people to call me, something with no awkward connotations, and easy for me to remember. I had recently re-read Ronia, the Robber’s Daughter, by Astrid Lindgren, and it occurred to me to use her name. Happy coincidence.
Mine is from the book Eats, Shoots, and Leaves. In the beginning we are asked to let our Inner Sticklers out and not let abuses of language idle by. It was that book that awoke my need to proofread and it was fresh in my mind when I registered here. Also, I am one of the more knowledgeable people when it comes to proper spelling and grammar in my group of friends. (Not here, though.)
Well when I first joined up, I never thought I’d still be here 5 years later… So I just picked the first thing to come to mind that wasn’t my usual “handle” which was a variation of my real name. So I randomly picked “nyctea scandiaca” which was the scientific name for the snowy owl. I happen to be a big bird fan, and I especially love owls, and thought the scientific name sounded kind of neat.
Well, long ago, when it was a going concern, and at least half as fun as this forum, I was a regular on Yahoo’s Religion Chat Room #1.
I was (at the time) a curator of a military mueum, and my web page at the time featured me in a three peice suit holding a Bren Gun (Antique machine gun) looking bemused.
I was also into yoga and enjoyed puns… One of my Alternate names was “Assana Banana”
regards
FML
Mine comes from the job I was doing at the time. I was working with NEC on their undersea fiber optic cable projects. Submarine: sub-, Fiber Optics: -light.
It had nothing to do with SF or space travel, and it wasn’t until several moths later that I noticed that connotation.
The short answer is that mine is taken from the 19th Century British service rifle of the same name.
The longer answer is that it’s sort of a clever melding of a sophisticated drink with the name of a British Small Arms Factory to create… actually, I don’t know where I was going with that beyond trying to come up with something other than “It’s taken from the name of a 19th Century British service rifle.” 
Mine comes from the title character in The Man Who Never Missed. I was feeling lazy the day I signed up and so I grabbed a book at random from my bookshelf and took my name from there.
I was watching a movie when I finally signed up after lurking a few years. Can you guess which one? Actually I chose it so I could use this sig line:
Like Aziraphale, my handle is from Good Omens. Not sure why it occured to me, as I haven’t seen the book in years. Essentially, I wanted a name with a touch of menace, and since the literary The Them are kids, it also reflects the fact that I behave like a fourth grader, when I’m not acting like a two year old.
I came very close to being 69X drive, but it just didn’t reflect the real me. Doubtless, someone in the Dope will figure out where that one came from. 
I guess mine’s sort of obvious. I was lurking one day and wanted to answer a question about an old Plymouth, so I registered. Then it dawned on me that I needed a name. I chose one that’s somewhat descriptive: I don’t have much, but I have three acres and I have a little pickup truck, and that’ll do. The phrasing came from ‘40 acres and a mule’, which a friend and I had talked about earlier the same day.
Cate Ayo is a tribal name, Cate= Red, Ayo-Hawk.
Mine is from a quote by David Lee Roth regarding the then-proposed Van Halen reunion. I guess the mixed metaphors just appealed to me, as I consider VH to be average.
I’m in Siam, although my real name is not Sam. But I like the alliteration. Thailand Ted does not sound as good, and there’s already a Bangkok Bob over here, but I would not have felt right about lifting his name. I like Siam Sam better anyway. 
I just wanted a short nickname.
Shortly I was but a wee high school grad who’d come from small town Texas to big (big-ish) city Austin, I was given the opportunity to take a tour of Origin Systems.
Back up a step.
When I was eight years old, my father bought a computer for the house. He took me to Sears to buy computer games. “Don’t let her get a bunch of games,” said my mother. “I don’t want her inside all the time playing video games. One game, an educational one, should be fine.”
So we went to Sears, because that’s where you got computers and games for them at that time. We looked over the games. I was feeling a bit low, since I already had a taste for fantasy and adventure-type stuff. Dad considered, finally pulling down a copy of Jeopardy. “You like this show, right?” he inquired. “And it’s educational enough.”
“Sure, that looks good.” Well, it might be fun!
“Great.” Pause. “Get two more and don’t tell your mother.”
My two delighted choices were The Crimson Crown and Ultima 5, which puts a definite age on me.
I played Ultima 5 for years. I never beat it until I was an adult. It gave me nightmares and I thoroughly enjoyed it. I got pretty crazy about the whole series and desperately wanted to meet the person who’d created it all. I still could not quite comprehend that this was all done by real live people who weren’t much different from me, or at least much different from how I would be in another ten or twenty years.
(For the people who have read this far, yes, there is a point.)
So I hopped on board for the beta tests for Ultima Online, what I thought would be the peak of all gaming forever and ever. I made friends with a few Origin employees and one of them offered to give me a tour of the facility.
When I was taken through the gamemaster floor, I saw a cubicle that was absolutely crowded with figures of all sizes, from big action figures on down to gumball-machine sized figures. We chatted with the fellow for a few moments, and when I left his area, he called me back and gave me a small handful of tiny plastic ninjas, just the sort you see in Tiny Ninja Theater. I’d never seen anything like them. I had a souvenir and I was utterly charmed. “I got ninjas!” I kept saying to myself.