So, so many things.
1. Anything that involves catching or hitting something. I’m blind in one eye so I have no 3d special perception. So I am useless at tennis, squash, football and any other sport involving a ball, puck or other flying object.
2. Languages. I love language, I find it completely fascinating and I can spend hours reading a foreign language dictionary just for fun. But I am so hopeless at memorising vocabulary that learning a second language is impossible for me.
3. Cooking. I utterly hate cooking, and I don’t have the patience to learn to be any good at it.
4. Playing any musical instrument. I seem to lack the motor control required to co-ordinate my fingers to do the right thing. I learned guitar for a year and was no better at the end than I was a week after I started. I can’t master doing different things with each hand, or doing something with my hands while I’m doing something else (singing) with my mouth. I can’t touch-type either, for the same reason (but I’m a damn fast two-finger typist).