1. When you know how to
do something really well, but when you try to show people you suddenly can't seem to do it.
2. When you can do something without
thinking about it, but when you consciously engage in said activity, you constantly fail
at it.
I tried to show off to my friends how well I could
ice skate, but I was struck by an
acute case of muscle memory-loss and I fell
on my ass. They wouldn't believe that I was ever good at it afterwards.