C, G, I, Q, U, W, X
What trait makes these letters different than any others in the English alphabet?
They have dual sounds?
They taste great and are more filling?
They’re floor wax and dessert topping!
…No, not quite. 
Well?!
(not such a “Quick Riddle” afterall, huh?)
They’re the only letters that can spell Quigwixuc.
FTR, a Quigwixuc is a tall hairy neaderthal like creature with three thumbs and four asses. It should not be mistaken for its relative, the Kwijibo.
Um … Letters on your license plate?
Middle initials of every President?
Only letters your three year old niece can’t pronounce?
When recited backwards Bloody Mary comes out of the mirror to hack your nuts off?
I give up.
So, don’t leave us hangin’ what is the answer??
Um, they weren’t originally letters in the English alphabet ? shrug best I can come up with this early in the morning.
They are letters that, when played backwards, sound an awful lot like jazz?
Such creativity.
Actually, as best I can tell, those are the only letters that can be spelled phonetically without using themselves in the spelling.
C – see
G – jhee
I – aye
Q – cue
U – yoo
W – dubble yoo
X – ecs
Does that answer satisfy anyone? 
eph?
wi?
No, not really.
Define “phonetically”.
What about:
J – dzhay
K – cay
Y – wie
???
You are all so STUPID 
they’re the only letters in the alphabet that are symetrical…
Man, Great Phil.
Nothing like taking a little while to warm up to the crowd. And vice versa. Stop being so shy, will ya?
Welcome. (I think.)
haha I never actually mean anything I say…now tell me the answer to this riddle or I’ll punch you
How do you pronounce “???”?
Bastards. I said it was a quick riddle; I never said it was well-thought out.
huffs away grumbling about his forgotten Trivia Challenge thread
So, are you saying you didn’t have an answer?? What is the answer you were looking for?
I was saying that scratch and Dinsdale showed me that my answer wasn’t nearly comprehensive. I’ll flush with shame forevermore, and can never speak to the two of them again.