Lots of different things. One thing that happens a lot is I'll develop new academic interests and be convinced that I'll be a leading expert in those topics in no time. I'll buy lots of books, research equipment, and so on. I've easily spent thousands of dollars on books I've never read. Sometimes I go back and actually delve into those topics after a while, sometimes years later, but a lot of times I never do.

I've also started art projects, signed book contracts, signed up for various music lessons for several different instruments at once, all with the idea that I'll easily become a pro. It's especially embarrassing when I later have to go back and cancel all those obligations because I have neither the time nor the energy I thought I was going to have.

I also tend to become overconfident work-wise and take on more projects than I can manage, or e-mail colleagues about half-baked ideas that seem fantastic to me at the time. That can be embarrassing.

Often I'll also crave some sort of adrenaline rush and I'll want to do things like learn skydiving and the like, but a lot of times it turns out to be impossible to start the same day so I tend to take that energy out in different ways, like driving fast. In that same vein I often get lots of energy for sports and I feel like I could run forever.