Sometimes I'm just not in the mood to hear a story about a game that I wasn't in, especially if it's objectively a lot less interesting than the people who were in the game thought it was. Or, and this isn't true universally, of course, if the person telling the story, well, can't tell a story.
Are there any good tricks out there for changing the subject without making the person telling the story feel bad?
I always hold up the example of Eric and the Dread Gazebo as what a great gaming story should be: its not about your character, or their stats, or their epic quest to save the princess, but about a generally funny or interesting moment that occurred due to the game mechanics and human fallibility. Those sorts of things are universal, while knowledge about your campaign isn't, which makes most stuff that happens there an inside joke.
Obviously you understand this, but I would basically say, "Hey, let's talk about the game rather your story and character than I have no foreknowledge of", or just generally try to steer the conversation in a different direction. I've found that as long as you aren't painfully blunt, people will understand because pretty much every gamer has been on the receiving end of a long, uninteresting game story.
If you might be interested in joining their game at some later date, you could tell him that you enjoy playing the games more than you enjoy vicarious recounts. There's certainly enough understanding of this idea from actors and athletes that he shouldn't feel insulted.
