Whistle, period. Turn even garden-variety non-gymnastic cartwheels - I’m incapable of getting my legs up over my center of gravity, even briefly.
In addition to the aforementioned two-finger whistle, wrapping gifts and rolling Rs, I cannot snap my fingers. At all.
Is it the toothbrush, or the foam? If the latter, I have that trouble too, and it’s gotten considerably better since I started using toothpastes without sodium lauryl (laureth?) sulfate in them - it’s just a foaming agent. Among others, the Trader Joe’s mint and baking soda toothpaste, at least one of the Rembrandt toothpastes, and Sensodyne Pronamel are brands that don’t/didn’t have it. If you see any designated as being “canker sore control” versions, that is another good sign, as the SLS is thought to trigger them at times (and frankly, I haven’t had any since switching types).
I can’t do any whistling that involves fingers, just the “put your lips together and blow” milder form of whistling.
Oh, but as for gift-wrapping, the wife actually likes my clumsy attempts. She thinks they look cute. 
Ride a bike or whistle. Or tell you anything about key, scales, bars, measures, etc.; I just don’t understand that musical stuff.
Depends on the branch. In the Navy, yes, because Captain is (IIRC) their equivalent to Colonel, and there is no such thing as Major, but Navy Captains outrank Majors from the other services. In the other services, no; Captain is a low officer rank.
I can’t whistle or swim or many of the things already mentioned, but I’ve been working on swallowing pills. Just in the last 2 years or so (and I’m 31), I’ve gotten to where I can sometimes swallow them with plenty of water (if they are fairly small like an advil). The problem now is that when I don’t swallow them I usually gag and sometimes throw up. So I have to gauge the size and if I think I can do it, then either bite them into smaller pieces to swallow or just chew them up, all while drinking a lot or eating sugar!
I also can’t tell my right from my left. I’ve learned to compensate because I wink with my right eye (and since I’m right-handed I can tell which way is which if I have a writing utensil). Most of the time you can’t tell, but sometimes when giving directions or something like that I mess it up.
Oh yeah, I thought I couldn’t swallow pills larger than an oral contraceptive pill without water. That was until I had the worst migraine I’ve ever experienced (as in, curled up in the car crying with my hands over my eyes and I couldn’t shut out enough sun using just my hands) and gulped down four Aleve caplets without a bit of water. Turns out it’s really just the uncoated tablets that ick me out because they taste awful and get stuck on my tongue, but coated caplets or capsules have enough of a buffer to get them down without tasting nasty.
Case in point. I lost you after “In the Navy…” :smack:
Get hired to a decent employer at a living wage. 
Can’t snap my fingers, or roll my r’s.
I can touch my toes fine, I just have to bend my knees to do it. I’ve been like that as far back as I can remember.
I can’t bend the distal joints of my pinkies without also bending my ring finger, and there’s not much strength to the bend until the middle fingers get involved. It’s supposedly one of those genetic things.
I can’t whistle, which is frustrating because I always have a melody in my mind. I just do melodic blowing, clicking my tongue against the roof of my mouth for percussion.
I also can’t snap my fingers, I have really small wimpy hands.
I can’t skip rope, swim, two-finger whistle, roll my r’s, never could cartwheel (though I think I get a pass on that now being 41 and all) —I’m sure as this thread progresses I’ll be reminded of lots of other things I can’t do too.
I can’t ride a bike. I just never learned.
I can’t swim underwater without holding my nose.
Ah, but can you swim above water without holding your nose?
I can’t tie my shoes with the “loop and swoop” the way most people do. I make two loops and tie them together. Attempting the loop and swoop will only end in tears.
For all of you who have difficulty swallowing pills:
My dad taught me this when I was about 6 and was afraid of swallowing a vitamin. Next time you’re eating a meal, preferably alone, take a large bite of food, chew and just as you’re about to swallow, spit it out instead. Make sure you didn’t chew it like crazy, just like normal.
Take a look at the amount and size of the food that you were about to swallow and compare that to the size of the pill.
That stuck in my head and I was never afraid to swallow a pill again.
Another non-whistler. With or without fingers.
FYI, I DID come upon a miracle product in a store to help me. It’s called a whistle.
I never learned to read or write. Ever.