I'm fiercely passionate when I get excited about something. Usually those passions involve some sort of athletic or intellectual challenge. Anything from snowboarding to quantum mechanics, I derive happiness by immersing myself into difficult tasks.
If it means anything to you, my MBTI is INTJ. While I don't think any one person can be categorized into a rigid personality type, it is a good place to start.
-debating with myself on whether or not to get a twitter account.
-playing sports/working out
-internal dialogue (too much probably)
Knowing A LOT about very few things... Ph.D.