I love nuclear physics. Constantly reading books and studys on it.
/nerd
For me it's astro physics. I'm so fucking baffled by the universe and the concept of space, time & gravity's effect on both, and I can't get enough of it. I love Steven Hawking, the guy just makes my brain hurt. I always say to my friends "you know what really pisses me off...?? ...space! It's just too damn big!". It's a shame I hated math in school, because I would have become a physicist if I had been any good at it.
I love randomly quoting every movie ever made with my sister and couple close buddies. I'm talking mainly old (bad) action movies like Lethal Weapon, Predator, Commando, Point Break, etc. It drives my wife insane that I can rattle off line after line of these old flicks.
I also love 80's hair metal. That's about as dorky as you can get, but that was my early teenage years and I was obsessed with Guns & Roses, Metallica, Poison, Motley Crue, Winger, Skid Row, Warrant..the list goes on. Sirius 23 Hair Nation, best channel on Sat Radio.