I’m not talking about the physically impossible; none of us can fly or turn invisible. I’m talking about things that many, or even most, people can do. For me, there are a few. I can’t do any maintenance on a vehicle more complex than changing the oil. My dad and brothers tried to teach me. It looked simple enough when I watched, but I failed over and over. Math beyond first year high school algebra? Forget it. Read signals from someone with romantic interest? No, not even when someone who gave them told me later, or when someone said they just observed them (mostly Ms. P on observing them, but not always). Are there times when saying “I can’t” isn’t an exaggeration?
Identify cars. I don’t drive, but still. I am astounded by people who can identify make, model, year. Not just that they can remember and differentiate, which IS wildly impressive. But also that they cared enough about something so mundane as to store endless knowledge based on minute differences. It’s very impressive to me. I could not do that, if my very life depended on it.
I can identify make and model. All I have to do is look at the nameplates. 
My husband is one of those “ID cars by make/model and at least a good approximation of year at a glance” types. I’m more on @P-man’s end of the scale.
I have yet to figure out rolling an r, which does not improve my Spanish in the least.
Identifying the cars is something I’m pretty sure I could do if I had the interest. The things in the original post I put some real effort into but just couldn’t get it.
I seem to be unable to cut a straight line with a saw and tend to be iffy with a knife.
There’s an exercise move called a “lunge”. I spent 20 minutes in physical therapy making pathetic attempts to make my body do this particular move, to no avail.
Think they’ll try to make you do it next session? There was one exercise I absolutely hated when I had PT for a frozen shoulder. I won’t say I couldn’t do it in the sense that I can’t throw a 90 MPH fastball, but it was way harder than any of the others.
I can’t navigate. I get lost on roads, I get lost in buildings, and I get lost playing video games.
When I’m lost, I consult my gut instinct about the correct way to go, and then do the opposite.
Swim. I can do the basic strokes and can tread water, but I’ve never been able to put my face under water without getting water up my nose. I’ve tried and failed many, many times, including with swim classes and friends and… I think my nose is just not shaped right for it or something.
Also, crochet. I don’t know that I would argue that most people can do it, but I would think most people can do it if they’re taught how. I can knit, braid, macrame, and do cross stitch and fiddly origami, so I don’t generally have problems with fine motor stuff/following instructions. But for whatever reason, I just can’t get my head around crochet. I’ve lost count of how many times I’ve tried. I probably actually have a crochet hook in the drawer next to me and maybe I’ll try AGAIN. It’s absolutely frustrating because I can’t see any reason I should have such difficulty with it, but… I do. Maybe I need to find an actual human person to teach me instead of relying on books/YouTube/Googling “How to crochet.”
My sense of direction isn’t great (probably connected to my problems with spatial relationships in general). Thank Jah for cities built on grids.
One hour down and nobody has said, “you could do it if you kept trying?” I’m shocked, I tell you. 
I am terrified of putting my head under water without plugging my nose. I was recently practicing this emotion regulation technique where you put your head in a bucket of ice water and I had such a hard time with it, because I was so afraid I would snort water up my nose. I don’t know how people do it. How do you just not immediately inhale water?
I have always had exceptional upper-body strength for a woman, but I have never been able to chin a bar, even when I weighed 60 pounds less than I do now.
Do you have long arms? That can make it harder. It makes both push ups and pull ups hard for me.
I can’t dance. Period. Whenever I try, I look like a whale out of water. I’m only half-joking when I say I’d rather spend several years in a Siberian gulag than to have others put the spotlight on me on the dance floor.
Even though I am a Star Trek fan, I cannot do the Vulcan V-shaped “live long and prosper” salute. The way the ligaments and webbing on my hands are structured just don’t allow for it.
I can dance, but very badly. I play a great rhythm guitar, but my feet won’t do what my brain says do.
I can’t whistle or roll my R’s. I can just barely say the word “rural”, but only sometimes.
I can’t keep the house clean and uncluttered.
I have a problem with “powerful”. Like GW Bush, I also have trouble with “nuclear”. I’m no fan of his, but when people would imply that was a sign of weak intellect in always smacked of elitism to me. Btw, JFK pronounced it “nucelar” as well.