My avatar is a pic of Me and my sig line is/are quotes I attribute to Myself 
I don’t think I’ve ever encountered another Sith Bunny, certainly not one with the Farce Power of Easter (all parents know the Easter Bunny is a Sith Lord)
Lots and lots of beckdawreks. They ain’t me.
I was beckdawrek when I was a tiny girl and my Daddy made up a little diddy about my name. He had nicknames for all of us.
So I got first dibs. Altho’ all those other beckdawreks don’t care. Stinkers.
I really don’t know. I ran across a different Dung Beetle one other time, on a medical forum asking the same question I had been going to ask! It turned out to be my mother, who “borrowed” my internet name because she didn’t have one of her own.
I am on the Unaboard too.
Other than that, zimaane is unique, as far as I can tell.
My real life name is fairly common, so it’s nice to be different online.
Would any one else in their right mind use btwm? No.
(Apparently, it has been co-opted once by a SPAM-mer, but my wife has alerted Google. Other than that, I’m all alone in the world.) <-- Mr. Magoo reference
Jet Jaguar and it’s variants used to be uncommon, but in the last 5-6 years it’s become so common that they’re pretty much always already taken. So in games and other sites I’ve started using a different name that’s based on a MST3K sketch, but not exactly the same as any of the names listed in that sketch. That one is unique and always available.
In 1999, Internet was made out of wood and bronze. But at least forums were generally unmoderated. 55 threads about me selling only spam follow.
I had very very many nicknames in different places. Sometimes I changed my nicknames weekly.
I guess mine was desirable for hospital planning people. Who knew? https://windsormegahospital.weebly.com/
as far as I know I am the only rsat3acr. Some may remember I am a dentist. There is a dentist in CA with my same first and last name. Only about 8000 of my surname in the U.S. so I find that interesting.
Ronald Jones was the sonarman on USS Dallas (Hunt for Red October), I always conflate them into…you. :o
Do you look like this, from the front?
Apparently there is someone else who beat me to Twitter with this moniker, which has been my primary nom de net since 92 or so and alt.callahans.
He’s the drunken asshole. Honest.
I’m also on flyertalk, the social media site for frequent flyers, but I very very rarely post there.
My name has nothing to do with me being an author, but there real authors with the last name of Balk. IRL there was someone in the city I lived in with my name who was murdered and it made national news. I had calls from across the country to check on me.
The Great Space Coaster is mostly forgotten, but not totally obscure. There are many variations on the name of the wildebeest newscaster floating around. The precise way I have it here, all lower case without a space, is used by people other than me on Twitter and Instagram and probably most other sites. But it’s mine here and at a large, prominent aggregator site.
Well, no gnus is good gnus. 
When I joined the board Bubba was the name of my dog who I occasionally referred to as Bubbadog.
I was unaware that the name would be popular with others and as such the Straight Dope and Giraffe’s board is just about the only place I have this name.
Anywhere else I try to join I usually get told that the Bubbadog username is taken.
Bubbapuppa is less used so oh a few sites I’ve taken that username.
I didn’t expect to find any other Pixel Dent’s but apparently there’s a dentist in the suburbs of Chennai, India called “Dental Pixel Dent Care” which is pretty close.
As far as I am aware, I am the only Suburban Plankton out there, though in most places I’m suburbanplankton.
There are several, because it’s such an obvious handle for anyone named Carol who either loves Egypt or lives in Cairo, Illinois. (Oddly, neither of those conditions applies to me - I just happened to be living in Cairo when I first took an on-line user name, and as I’m an Indonesia lover, the name was kind of a nod to the (in)famous Surabaya Sue). A CairoCarol has a Twitter account and that’s not me. Apparently there are 4 (?) Facebook CairoCarols, none of whom are me.
My name IRL is also pretty common. People with my name litter the internet.