I don't really fit too much in to the gamer stereotype, so it's not really important. When I'm with my best friend, we'll discuss things like politics, Wikileaks, uni, gaming, movies, friends, recent events, etc etc. Our gaming discussions get pretty hardcore, but we're in to stuff like WoW, S.T.A.L.K.E.R, Elder Scrolls, Fallout, Bioware games, and whatnot. So not really anything to be ashamed of in public. I can talk with most scenes around my fair city.
I know a lot of hardcore kids, so I always get along with them. Usually talk about dubstep and alcohol abuse, which I'm fond of, and they warm up to me, usually. I'm a funny guy, so I usually charm people over.
Gangsters: Don't really associate with them that much, but again, dubstep and alcohol abuse. Seriously, those two topics will allow you to talk with a lot of different groups.
Hipsters/Metalheads: My roommate knows most hipsters and metalheads in Canberra, so that always helps. I find that metalheads are usually pretty chill dudes, if you get them when they're not talking about music. Getting in to a musical discussion with a metalhead, (which happens all too often) is an uncomfortable and alienating experience. Do not want.
As for Gamers (minority) and other, non-genre-specific folk, I rely on wit and charm. Mostly depends on how much alcohol I've consumed, but once you've broken the ice with someone, it's easy to talk to them. I've made a lot of friends from random, beer-fueled ramblings. And hundreds of great stories. Hell, last party I went to, I passed out in a toga and got graffiti-ed with a Sharpie. And made friends.
I'm also delusional as to my own popularity and self-worth, so take that with a grain of salt.
Edit: Hilarious side note. I once accused my roommate of being a hipster, and when they rejected my carefully thought out hypothesis, I stated "Perhaps the most telling sign of a hipster, is that they deny being a hipster." This brought forth murmurs of assent from our mutual friends. When she decided to counter-accuse me, I dismissed it with a confident and quick, "No, that doesn't really work for me."
And all of our friends agreed. Winning!