I'm a big gaming nerd, I'll admit. Still, the day I bought God of War Collection from Gamestop, some military guy walked up to me and started talking about how nobody plays games more than him, which games he liked more than others, about Pokemon (!), and about Indiana Jones and Avatar (!?). I humored him with conversation but I thought to myself, "I hope to God I've never been this annoying."
Games are cool but like anything else, a little too much knowledge about a subject makes you appear a bit geeky. Sports, comic books, cars, anime, or whatever. When you first approach someone, you have to introduce your interests in moderation.