I would have to vote golf, at which I play appallingly or not at all.
You wouldn't think it would be that hard, after all the ball isn't even moving when you strike it.
I had a friend liken it to chopping wood with an ax, but being able to hit exactly the same spot every single time.
The whole motion of the golf swing has so many components it is mind boggling. The whole body has to move in a synchronized motion and any one part not in place will mess it up...the grip, arms, body twisting, knees, feet...
Then to top it off you have the different clubs, and need to be able to know what sort of loft and distance you can achieve, judging the slopes and distances of where you want to land. Then you have to putt, which sucks.
I hate it.