Taking a paper and pen on board a 12 hour flight and writing code on how to figure out how to solve a particular coding problem. The people sitting next to me were wondering what I was doing and frequently stared at my paper. One of them did end up asking me what I was doing and laughed after I explained it to them. Actually, I used to do that a lot... in class when I was bored or when I didn't have access to a computer.
Getting into a big argument with my friend on which is a better graphics card and how to code a particular problem.
Talking with my friends about the latest slashdot stories.
Being the goto guy for whether a game for any particular system is good or not even though I may not have the game/systems.
Being able to recall obscure facts about past games/game designers. I remember when Doom 3 was coming out, I spent about 1 hour telling my co-worker about the history of iD.
Keeping the original packaging of all the games I've owned.
My Mom was learning metal-emboss art and I convinced her to emboss Sonic the hedgehog... it came out pretty cool and I hang it near my computer.
Frequently upsetting (not intentionally) Professors who teach programming at college by asking questions which they did not know answers too. After the first few days, I know whether or not I'm getting on the nerves of the teacher and stop asking questions. However, the really good ones appreciated and encouraged me to ask questions... when they didn't know the answers, they would flatout say that they weren't sure and they promised to get back to me.
Owning every Nintendo system from the NES onwards (except the virtual boy.. wasn't in the country at the time, so it wasn't really my fault

).