What are some skills/abilities that you have that have rather limited usefulness, and may actually be harmful?
For instance:
I have no trouble, whatsoever, not eating. I can go for days and eat nothing. Obviously, this isn’t a particularly useful skill, unless I wind up stranded with no food for a while. 
However, I’ve had quite a few people be totally amazed that I can not eat, and not notice, for a really long time.
How 'bout you?
May actually be harmful, you say?
When traffic slows, I can usually tell if I have to keep my car in gear, brake, or if traffic will slow gradually and consistently enough that I can coast without either engine-braking or using the gas to keep up my speed. Sometimes I can coast for nearly a mile without disrupting the flow of traffic. But they say that it is better to keep your car in a gear in case you need to accelerate quickly. It’s also supposed to save gas, as you are using the car’s speed to keep up the revs of the engine rather than using gas, but probably not in the case where you want to coast rather than engine-brake.
In high school, I learned to flip pens. It became a habit for me, and pretty soon I was flipping all the long cylindrical or rectangular things I got my hands on. I realized it was a problem when I started to become proficient at flipping knives. There are no situations in which the ability to flip knives does anything but put the lives of those near you in danger.
I can’t smell bleach. I worked in research animal husbandry for a year and half - spraying down enclosed and unventilated rooms with bleach three times a week.
It works great in chemistry labs when everyone else complains about the smell.
But sometimes if I’m cleaning and using anything with bleach as an active ingredient, my roommates have to come in and tell me that if I don’t open a window, turn on a fan and leave the room for 15 minutes, I’m going to die just from the fumes.
I concentrate so hard, so hard, so hard, that Mom says I make her afraid one day I’ll concentrate real hard and actually get smaller. When she calls me and I fail to respond, she says I’ve “gone into soup-cube mode”.
It’s gotten me in trouble with people who couldn’t grasp the concept of “if I’m doing something and you need to talk to me, use my name as the first word in your paragraph and don’t say the next word until I answer.”
Another: I take lots of things much more mildly than other people expect. While this comes in handy in emergency situations, I’ve often offended people who thought my response wasn’t earthshaking enough. Well, so-rreee, but if you say “we’ve moving”, my autoresponse is “oh, that’s nice! Where to and when? Anything I can help with?” I am not, now or ever, tacking three exclamation marks after “that’s nice”.
I can sit and do pretty much nothing for long periods of time. Of course sitting in front of the computer or tv is helpfull but when I get into a good book I’ll just sit there and read it all day too. Couple this with my ability to consume large quantities of food at frequent intervals and it gets potentially harmfull rather quickly. But I did buy some in-line skates this week. So far only very short sessions because it seems really hard on the muscles running up the side of my shins. I hoping that improves along with my technique and endurance. Stupid food, it’s too darn delicious. I would be happy to trade dubious skills with you alice. No deal? Damn.
Well sure. Until you pass out at Stampede because you forgot to eat for a couple of days, and you wind up lying in a pile of discarded mini-doughnuts, wondering what the hell happend.
Remember the scene in Aliens where Bishop does the knife-trick by stabbing the table really fast between his fingers?
Well, as he picks up the knife, he gives it a twist and it spins like a top, point down, on his hand for a second or so.
I can do that spin.
I can do the not-eating thing for days. It’s all that’s left over from being poor. My wife says she doesn’t know how I can do it, as after a certain amount of time, she just has to eat something.
I can do backtiming, which is the art of figuring out when you have to start a piece of music playing in silence, to fade it up and have the end happen at a precise time on the clock. It’s only good at my job. It’s a skill I never have to use anywhere else.
I do the not eating thing too. It makes my husband crazy. Seriously crazy.
Don’t you just HATE when that happens? 
I can move really quietly if I so desire. Sneaking up on people who do wish to snuck up upon can have bad consquences.
I have an amazing knowledge of mythology and etymology. In fact, I tend to know exactly where various words / phrases / stories come from, and can drone on and on / ‘geek out’ ad infinitum over such things.
You’d think it’d be helpful.
Somewhere.
Nope. Just bores the hell out of my friends.
Ok, ArrMatey, can you tell me something- what is the etymology of the word “etymology”? I’ve wondered that for years.
I can eat almost anything completely silently.
And I know most of the geography of Africa.
I can tie a hangman’s noose. Trouble is, am almost never called upon to do so. However, if I’m ever invited to a lynching party…
I can recite the “Peter Piper” tongue-twister faster than anybody else I know. Trouble is, it’s difficult to work into ordinary conservation.
I know the entire dirty version of “Dangerous Dan McGrew.” Same trouble as No.2
If I’m walking hand in hand with someone, I can tell if her shoes are hurting her feet or if she’s in pain of some other kind by how she periodically grips or squeezes my hand.
Mmmmmmmm, mini-dougnuts.drool
Now you went and made me hungry. No, wait. I’m always hungry. Nevermind! I would suggest taking a really hungry guy with you next Stampede. You’ll be sure to get reminders to eat long before you find the mini donut trailer.
Well, I am capable of peeing sitting down, however this has limited usefulness, as it is much more fun to just let it fly. (outdoors is preferable)
Like Regallag, I can walk very silently, but without even trying. If I had a nickel for every time I walked up to someone in their cubicle or office and started speaking to them, and they jumped in that “aaahhh!” startled way, and said “oh my God, you came out of nowhere!”, I’d be a rich man. I guess I just walk very silently, or something. I’m actually not so sure that this is a skill…
According to Zobmondo and Scruples, I’m a borderline sociopath.
I can dislocate my arms at the shoulders, at will, with no pain.
I can build a simulated nuclear bomb in about 45 minutes. A little longer, if I need to do the paint and nose art.
You know the game Call of Duty? I once got to the top of the north tower of the “Pegasus Bridge,” and sniped a BUNCH of Germans in the vacant lot on the far side of the river. With a bolt-action Enfield…using the iron sights. ("‘JFK Reloaded’ was a fag.")