I can do a track stand for as long as most traffic lights take to turn green. One thing I never could get the hang of is riding a unicycle. I spent several hours trying and finally gave up. Also a cool trick I never could master for more than 30 seconds or so was riding a bike backwards ie sitting on the handle bars and facing the back of the bike and pedaling. I bet I spent well over 20 hours trying to do it and usually after 15 or so seconds would have to put my feet down. My uncle could ride a bike that way all over the place even when he was well into his 70's. He never got tired of telling people his family was too poor to buy a bike with a seat so he had to learn by sitting on the handlebars. I think he got a kick out of the fact we all tried and could never master it.