I suck at numerous things mentioned already in this thread. However, I reached my nadir in high school chemistry class. Mom holds a chemistry MS, Sis holds a physics MS, ruadh had to cheat on her exams to get a D. And I managed a 4.0 for my last six semesters of university, so it’s not like I’m stoopid or anything. I just cannot for the friggin life of me understand chemistry.
Attacking people, beating them up, shooting them, stabbing them, biting them, beating kids, screaming & yelling,those I suck at doing cause I just can’t do them.
I really, really suck at math. Like really. I add and subtract on my fingers. I can’t divide without a pen and paper. I memorized all the times tables from 0-12, so that’s easy. But algebra? Forget it. Calculus? I managed to graduate from college without ever having to even touch pre-calc.
In the same line, I suck at logic and debate. I don’t debate, I argue. I am a conversational guerilla when it comes to debating. I am insanely irrational at times, “this equals that” logic doesn’t usually make sense to me.
I suck at mapping. Not usually a problem, but in archaeology, it kind of is. I used to think the compass points were relative to me (i.e. in front of me is north, behind me is soutn) so I get confused. When I map the slope of a pit I’m digging, I almost invariably do it backwards.
I suck at most sports, except soccer and track. I can’t throw, catch or hit to save my life.
Planning? Forget it. I don’t plan. I do. Which makes my life kind of messy at times. I couldn’t ever be a manager or director of something, I’d have to write out plans and stuff. Ugh.
I can’t snap my fingers. There’s a slight, almost-snap with my left hand; nothing with my right. My 2 year old recently learned to snap better than I. Also, I can’t whistle.
I tried to play pool once. Now, no one with an astigmatism like mine is ever going to excel at any sport, particularly those requiring depth perception, but this was just laughable. Also, I throw like a girl.
ruadh, I’m with you on the chemistry issue. I like to think of myself as a reasonably intelligent person, but I could not, for the life of me, understand high school chemistry.
Although I have a BA in English, I cannot spell. I have a dictionary next to the computer at all times, but I shudder at what I must miss.
I’m absolutely awful at time management.
Completing computer games. I have copies of Warcraft, Starcraft, the entire Legends of Infocom collection, and the first five Might and Magic games installed on my home computer, and of all of those games I have finished exactly one of the Infocom games, and that’s it.
(I’ve tried to improve both of those two failings above, but unfortunately improving one tends to prevent improving the other 
)
I’m also, for some reason, really bad at tying my shoes. Let history judge me as it will.
I can’t swim at all (I’m hydrophobic).
I am soooooooo bad at sports, I was literally picked last every single time for sports at school. And the Cross Country is a hell I am infinitely grateful I left behind.
But the thing I suck at the most is getting women to like me - and that seems to be a terminal problem.
Hydrophobic?
Do you take showers?
Really now? 
Coulda fooled me.
I suck at drawing. I can kind of sketch something better than stick figures, but it’s sucky.
Harmonica ought to be easy, it’s just suck and blow, but it’s one of the few instruments I have tried that I am terrible at. I can still get the notes, of course, I play by ear on EVERYTHING, but the music is just horrendous.
I can’t whistle with a blade of grass or my fingers.
I am awful at most sports, especially baseball. Field hockey and lacrosse are ok, but baseball, softball, football, soccer, ice hockey (because I can’t skate), you name it I probably suck at it. I’m not even that good at foosball. Table hockey’s a good thing, though.
I don’t take compliments well at all. I tend to stammer and look at my feet, then say something disparaging about myself and change the subject.
I have difficulty with any math requiring beyond that you use to balance a check book. Really, really bad. Took algerbra 3 times, flunked every time.
I have difficulty with women… some of them really like me, but someone better always comes along… ah well.
I can’t draw, but I can do fantasy mapping… go figure. The best I can do is stick figures, and not very good ones of those.
I have no self motivation… I’ve been planning to get to the gym now for most of a year, an it looks like only now will I start going. Sigh…
anyone else who knows me probably has a long list.
My handwriting sucks big time. I am, however, able to fire off my signature in one continous line.
I am the anti-Norm. I suck at woodworking. I couldn’t cut a straight line if my life depended on it.
I won’t list stuff that’s creative in nature (singing, dancing, etc) because I don’t have enough room.
Yeah, of course I take showers. It’s not like I run screaming from water and cower in the corner. I only do that with big barking snarling dogs, and spiders.
I probably don’t enjoy showers like some people do. But you know, they’re a necessity.
Having said that, I have this skin condition - eczema - and it is recommended that I do not bathe as often as other folk. i.e. not daily, but maybe two or three times a week instead. Otherwise it dries my skin out.
(Perhaps this should be in the TMI thread)
Construction work.
I hate the heat, the noise, have problems measuring and cutting a straight line and lack people skills when it comes to dealing with coworkers whose interests are beer, pussy, pot and fighting - in that order.
Agricultural work. (See above.)
Being a main manager: I’m too soft on people, forget to delegate authority and keep crappy records plus feel that if I tell them to do something, I have to be able to do it myself.
Commission salesman: I hate having to try to talk people into buying something, especially if I figure the product is crap.Rotten artist: I love the smell, texture and colors of oil paint, love the feel of brush on canvass but can’t draw worth a crap. My paintings are laughingly called ‘impressionistic’.
Anything mechanical. Hand me a hammer and I look for a extension cord and outlet.
Got a screw loose? Quick, get a rock.
Need to repair an eavestrough? Maybe staring at it for 45 minutes will help?
I can’t sing in key…I’m a terrible singer…but that doesn’t stop me.
I’m sure I can’t do alot of other things…but if you don’t talk about it, you don’t have to think about it.
I have a lot of trouble with math. Not only do I have a hard time grasping concepts in classes (every algebra course I’ve had was a living nightmare), but I also have problems with basic arithmetic.
I can’t whistle.
I’m a terrible dancer.
There are thousands of other things, of course, but these are the ones that spring to mind.
Drawing: emaciated stick figures are a specialty.
Following through on my initial enthusiasm for a project.
Choosing a decent guy.
Pretty much everything, I guess. shrugs
I suck at math. Not addition and subtraction, or even multiplication and, if forced, division. But algebra stumps me. I am fine with numbers, but start throwing letters in there and I get nauseous. Oddly, though, I aced statistics in undergrad. Go figure.
Anything art related. I can barely draw stick people. With a ruler, I can make a straight line.
Any math beyond first year algebra. I squeaked through trigonometry and geometry in high school.
Getting stuff done in a timely manner. I always leave things to the last minute, then pull an all-nighter to finish up.
Housekeeping - though with a 3.5 year old and 10 month old, they undo anything I do!!
–tygre
Keeping a social calendar of anniversaries, birthdays, etc. I’d probably forget my own birthday if left to my own devices. Fortunately, my husband is one of those people who has his first grade teacher’s granddaughter’s bat mitzvah date written down somewhere–and remembers to send a card.
Singing harmony. I can carry a tune pretty well, but I always get distracted by the main tune when I try to sing harmony. It’s too bad, because I’m a perfect second soprano.
Filing. This is no doubt due to the same genetic defect as the first one, but I tend to just leave large piles of things on my desk, rather that developing some sort of system for putting them away. Luckily this affects no one but me.