I used to know the armour thickness and slope (all sides, top and underneath), and armament, of every major German and British tank of WWII. And I used to be able to add up a column of 4 digit numbers in my head; if there were 4 or fewer of those numbers instantly, otherwise in a few seconds.
I can name the backwards ones, from since they first ran the race! So there.
Me? I can collate and staple with the best of 'em.
I have a very fast foosball shot in which I do not hit the ball, but accelerate it from a dead stop to frightening speed without giving any other indication that I’m about to shoot.
I learned to play with expert players, and if I actually swung back to hit the ball, they’d already be in position to block it, so I had to develop this “sweep” shot, which is really much more about strength than speed.
This may be correlated with my other least important skill: taking six years to get a four-year degree.
Bah, I can beat that. I can take five years to get a two year degree.
Damn public schools… we didn’t get the “how to get out of a DUI lessons.” 
I can solve riddles really quickly.
Well, actually, I’m not solving them. I just like to read books of riddles, and I always end up looking at the answers. It turns out that, up until you hit, like, puzzlehunt-level challenges, there’s only 2 dozen or so different riddles. And I can remember the answers to pretty much all of them.
Perhaps we were twins separated by birth. And possibly years – since I never EVER fell in my youth, but as I’m older and fatter I can’t always catch myself any more. The clock thing too. I never use an alarm even when I have to get up at unusual times.
Am I the only one who can spin a record album jacket on my finger for like, an hour or more? I’m not sure I can still do it, since I no longer have a record album or a jacket.
Damn. How are you with removing plastic wrapping from CD jewel cases?
Trying to do this pissed me off somethin’ fierce.
So i guess that’s mine: i can get really pissed off at the drop of a hat.
I do and frequently have.
It depends on when the birthday is, though. That’s a rather seasonal skill I have there.
Besides - getting the clovers from Germany to Seattle while they’re still fresh might be tricky. I’ll be happy to deliver them personally though, if you pay for the flight. 
Nope - only coal-burning power plants around here. But I do get that question a LOT. 
I agree that it’s a fun skill, but until lissener pays me to deliver a bouquet I won’t include it in my CV.
Hmmmm -
I can get the bolt into a C9 machine gun, even if it’s slightly bent, much to the irritation of the men in my section.
I can also manually load a magazine lightening fast. (these two may not seem useless until you realize how brutal I am at actually shooting the bloody things)
I have a great brain for trivia, if it’s obscure and I have read it or watched it, chances are I remember it
I can accurately fake many accents
No, I’m just not good at anything. 
Trying to think of talents I have that are in no way useful… Uhh, I can gift-wrap like a MFer! I can crack my knuckles by just bending the joints. I can eyeball a precise jigger even though I’ve never tended bar.
i can touch my left thumb to the inside of my left arm, and my right thumb to the inside of my right arm (not necessarily at the same time).
I thought of one more - I am very good at voice procedure and for some reason, my voice transmits clearly over the radio, even with weak and distorted comms…
This is a drummer’s coordination excersize. We used to do it spinning our fingers pointing each other. Start out your left hand if you are right handed, then start the right one the opposite direction.
Then pat your head whilst you rubbeth thy belly.
I can write in cursive backwards. Fear my skillz.
My useless talent is singing and playing Rusted Root or Jason Isabell songs exactly like they sound live.
My band does a crowd pleasing Carny Man - Cross Canadian Ragweed and Send Me On My Way - Rusted Root medley that gets them up dancing.
I also can hack antiquated devices to do useless shit, for example, changing channels on a VCR from the kitchen so that the VCR can be used as a head unit for a radio to be run through my television, and the radio is actually a tape deck ripped out of a 1987 Honda civic that is mounted in a box using a 386’s power supply for 12 volt coversion…
I have a way with dogs that gets them to like me for some reason, even though I am afraid of big strange dogs.
I have really great luck going to the post office/DMV/tax office.
We used to be able to hit people with sliced prewrapped American cheese down in the parking lot from the fifth floor window.
I won a karaoke contest with a three set linup: Fast Car, Scenes from an Italian Restaurant, and Angel from Montgomery, and I ordered two pitchers of beer while I was singing.
I was reasonably decent at hanging upside down from a tree and dropping eggs on cars when I was 10.
Funny, but that’s my record time, too.
There are only three things I’m good at, all magnificently unimportant.
One is reverse parallel parking. There’s some sort of circuit in my brain that just works out all the correct angles without my even trying. It’s odd because in all other respects, my spatial awareness is poor and I’m no-one’s idea of a particularly good driver.
Another is freehand bread slicing. I do wish this was a popular sport that attracted massive sponsorship deals. I can produce straight, even slices, time after time with any ordinary bread knife. I can do slices of any desired thickness, consistently, evenly and relatively quickly.
My third and final flourish of unimportant giftedness has been rendered obsolete by the passing of time, and is also impressively obscure. However, I was once a very, very good operator of an Aston 3 caption generator. Back in the day, this was a huge box of electronics, like half a fridge, hooked up to a keyboard and a preview monitor. It was used to super-impose captions during a TV broadcast. The one we used was a very temperamental bit of kit that often sulked and threw tantrums, but I could always get it to work even when the trained engineers couldn’t. And I was pretty nifty at typing out page after page of captions fast enough for a high-pressure live TV broadcast, without any embarassing errors.
I know, I know, it’s all just too impressive, isn’t it? Those wishing to touch the hem of my garment, please form an orderly line.