I never learned how to ride a bike. I just kept falling down (I was a bit accident prone when I was a kid, but I think I've outgrown that now).
I don't know how to whistle when I actually try (I have done it unintentionally a few times, but when I actually try to whistle, I can't seem to do it).
I also never learned how to skip.
It also took me forever to learn how to snap my fingers and shuffle a deck of cards, and now I do both of those in a weird way (I snap with my pinky or ring finger, and I turn my hands backwards to shuffle cards).