I should prob'ly start with my personal definition of 'geek', so you can, vaguely, get where I am coming from:
1. Someone with a level of knowledge/skill in a focused area, who's knowledge/skill is best shared with others having the same knowledge/skill; people without the knowledge/skill may feel left out of or confused by conversations in the topic.
Now, in general, people see geeky as covering the computer/gamer/costume/ "those weird people" categories. I think you can be GEEKY! about anything.
Do you love the subject whole-heartedly? Does participating in the subject make your world go SQUEE? Is sharing with others in-the-know one of your favoritest things ever? Does your enthusiasm show? Can people look at you when you're talking out it and think "Wow, they are really into this!", even if their eyes are glazing over because they have no idea WTF you're talking about?
Congrats, you're a Geek. Maybe you're a math geek, or am art trading card geek, or a urban chickens geek, but you've got geekdom down to a science. According to me, at least.
So, without more ado, here's my Topics of Personal Geekdom:
Best selling computer game of the 20th century. (It held on into the 21st, until the Sims came along) Myst and the follow ups; Riven, Exile, Revelations, Uru, & End of Ages hold a deep and abiding place in my heart. Just as some people can see themselves living in Middle Earth without batting an eye, the Ages of the D'ni are my second home.
My dad had the original D&D Red Box. Family Game Night was always a reality at my house. I've LARPED, I've RPGD, I've done MMOs. I love puzzle games and escape the rooms and things that make your brain go hmmmmmm. And, just within the last few years, I've started writing and creating.
Unicursal winding path, found in almost every culture out there. I've always loved the symbolism, and in the past few years they've become a serious topic of study and exploration for me.
Yes, birth. As in Women Having Babies. This is both my profession and my vocation, and prob'ly the only thing I love talking about more than Myst ;)
Other things that might come up are Storytelling, Smith-Magenis Syndrome, Arts and Crafts, Polyamory, Neo-Paganism and whatever else wanders through my brain this week.
So there's my geekitude, waving like a banner for all to see. A-frakking-men.