Something you’re just good at with minimal effort and/or you learned much more quickly than average.
For me, it’s paper snowflakes. My brain just seems to effortlessly figure out what cuts to make to the paper wedge to make it turn out exactly how I want it. Largely useless, but good fun and was a much-needed ego boost when I was a kid :]
I can make my balls dance.
Oh yeah, that too. I’ll sometimes do it when standing wait for something, like a lift. Hopefully it isn’t obvious from outside my trousers.