Also, grad students are really boring to people who are not interested in the same ideas. My husband cannot stand going to grad student parties; it's not because he feels threatened by how great and super-intellectual we are or that he can't keep up, it's just that departmental gossip and a bunch of talk about Kant don't float his boat.
I agree with Marigolds, I think in many cases people are just bored by certain intellectual and philosophical conversations in general. Even during my senior year of college and while applying to grad school, I slowly began to lose certain friends who just didn't care about politics the way I did, or the psychological/emotional forces that influence voting, etc. etc. So everyday conversations (with family
and friends) began to come to a halt just because I started watching Jim Lehrer, McLaughlin Group and the like, and found social critique more interesting than whose album is coming out. Not that I couldn't talk about Keisha Cole's new album, but after a while it gets boring and hard to "fake it" anymore, so to speak. I'd also feel a little bummed that I was there for someone, but they weren't really there for me when I needed an ear. I have one particular friend who I adore, but I know it won't work because our interests have changed so very much. I don't think she feels inferior or anything, she just finds me boring sometimes, and I honestly feel the same about her, although she's terribly sweet and we still go out every now and then (in moderate doses).
But I've also had the problem of a friend thinking that I thought I was better than her, and becoming cold towards me once she found out I was applying to grad school and not planning on getting a job after graduation. While I never talked about applying to grad school, didn't tell her what schools I got in (until I chose one and I just mentioned it to her once before she promptly changed the subject) she still found it necessary to tell everyone at a party that she had gotten accepted into the same school, after they begged her for months about attending, but rejected them because the classes looked too boring. Mind you, I'm omitting countless facts that assures this story was a complete fabrication, and it really disheartened me that she felt she had to do that. This was announced (of course) after the conversation came up that I was going to start a Ph.D and I guess I'd gotten too many congrats. We don't really talk anymore, but there is absolutely nothing I can do besides being there for her when she feels like talking again. But I know she won't be there for me and I'm not sure if that's even worth it.
Then again, there are friends who have completely different worlds from me, but we still enjoy each other's company and I can talk to them about my fears of grad school without being judged or asked stupid questions about my reasons. And I look forward to making new friends during grad school, on the inside and outside of academia, who will hopefully grow in the same direction that I am. Every change we make will probably lead to newer and broader networks of friends, and that's not a bad thing. D*mn, I wrote too much.