I’ve always been fond of those long, funny ones.
Really Not All That Bright
you with the face
It’s Not Rocket Surgery!
Least Original User Name Ever (who I often get confused with Really Not All That Bright)
Well, he’s back
don’t ask
Don’t Fight the Hypothetical
WhyNot
6ImpossibleThingsBeforeBreakfast
ComeToTheDarksideWeHaveCookies
There’s someone on here with one that’s like JustSomeGuy or It’s that guy or Hey, it’s that guy; I can’t remember what it is exactly…but he goes here too.
Oh, if you only knew what kinds of passwords those people choose!
Patty O’Furniture makes me laugh like a kid…
Sort of like the (as-yet-unclaimed-on-this-site) Seymour Butz:
–famous to all 10 year olds as the author of “Underneath the Bleacher Seats”.
(Get it? Huh? didja get it? Didja? Huh? Tell me!!! 
)
A new one here: Oops I Went Poopies
Master Wang-Ka
Labrador Deceiver
Dogbutler
burpo the wonder mutt
And everybody’s favorite:
Throatwarbler Mangrove
I’m rather like ratheravisciousgentlemen (IIRC). Just trips right off the tongue, doesn’t it?
I still miss Imthecowgodmoo.
Left Hand of Dorkness always appeals to me.
**Unauthorized Cinnamon ** intrigues me. What does one have to do to authorize it? How bad does cinnamon have to behave to be lose their authorized status?
I like the name Le Ministre de l’au-delà, because I see it as a reference to a composer I like. I’ve also met this board member in real life, so maybe I’m biased.
No umlaut for U is clever too.
I like most of them; at least better than 50%. It (how the various minds here work and how the handles reflect that) is one of the reasons I like this place.
Absolutely and without exaggeration everyone mentioned so far with the exception of (and apologies to) EmilyG for whom a simple reversal could easily rectify 
(And I like how you all just automatically did that.)
ClockworkMelon was the first name that ever made me laugh, and the Spectre of Pith.…took me ages to learn and now I’ve completely forgotten.
Maggie the Ocelot is listly because you can’t read that without being tickled somewhere, and Johnny L.A for no other reason than it’s hard to be cooler than that.
kambuckta because it also looks good written down, FloatyGimpy because Novelty Bubble should have some competition.
There are many more; the hilariously witty and the insanely creative, and just I’ll have to wait until someone else remembers them so I can go OH…YEAH! out loud, alone.
“Unauthorized Cinnamon” is the name of the seventh episode of the third season of the HBO series Deadwood. In the episode, it refers to, at a meeting of the town’s elders, the unauthorized offering of cinnamon as an accompaniment to canned peaches (which, because of the scarcity of canned goods in Deadwood, are themselves only available during Meetings of Great Importance – whenever my wife or I tell each other that we had an important work meeting that day, the other person asks if peaches were served). I’d link to the clip on YouTube, but it’s very, very, very NSFW. Unauthorized Cinnamon is a great username.
Another of my favorite usernames, not yet mentioned, is Go You Big Red Fire Engine. He/she hasn’t posted since 2006, but I still smile whenever I think of the username.
For sheer bizarre-ness, my favourites have got to be
Biffy the Elephant Shrew
Go You Big Red Fire Engine
A Sniveling Mess
And I had thought that there was someone with the posting name Salacious Integument – but Search attempts have yielded me nothing on that one: perhaps I imagined it.
(ETA: Gordon Urquhart beat me to it, as regards GYBRFE)
Thank you!!
He just joined yesterday; hopefully, he’s not a drive-by; you expect to see his hand extended when you open the thread; yes, it’s–
billfromacrossthestreet
I’m watching Curious George, so naturally I’m reminded of the Doper Furious George.
I’ll give a shout out to Qadgop the Mercotan. Very meta, since it’s not merely the name of an alien, but an alien in a very bad space opera being written by a character in another space opera.
Spiny Norman
PurpleCrackWhore
The user f. coli has recently graced us. I like that one.
My all-time favorite is/was Filthy Beast of Meat and Hair. With a wit to match his moniker. Sadly he’s not been seen in these parts for years.
I believe that’s Novelty Bobble. Which is still a cool name.