The Casual / Hardcore Divide
Perpetrators: Fanboys, Lazy Marketers
Worst Example: Half the threads on gaming forums
I don't know who to blame more for this one; the long-time gaming fans who insist that filthy casuals are ruining the industry, or the lazy marketers who constantly try to hand-feed neophyte players watered down experiences. Getting upset because someone isn't as versed in gaming as you is just plain stupid and counter-productive to them ever solving your so-called issue, and with marketers creating a very clear divide between games for newbies and games for experienced players, they're never going to cross that threshold.
Yeah, we all want to see the day when you can turn to pretty much anyone and play a round of Street Fighter just as easily as you could suggest watching TV, but that's never going to happen if we keep treating newcomers like another species. That goes for people on both sides of the fence.
The Solution: Stop segregating new players from the old ones and let people learn the fun that comes from more complex games