When I was around 15 I tried to master the controlled coin flip, having been exposed to the idea in one of the Stainless Steel Rat books by Harry Harrison. I reached around 80% success flipping for heads, so long as I used the catch-and-show method. It was easier with heavier and bigger coins, tougher with lighter and smaller ones. Letting the coin drop the the ground and bounce took me back to 50%.

Satisfied that it could be done, I moved on - never used the skill, except as a party trick.