People who feel happy, usually give off a friendlier vibe. If you don't smile, don't expect people to smile back. If you think sarcasm is funny, it's not. If you have no patience for anything, chances are you snap at people without realizing it. The list could go on... But I think the main thing is that whole cliche: Smile at the world and the world will smile back. It's actually very true.
Peale, you seem OK to me. I have a couple issues in social situations, and one of them can kind of be traced back to this hobby. I'm not into a lot of mainstream type stuff -I don't watch popular TV shows like 24 (I prefer documentary stuff like the History Channel), I'm not much into "stick and ball" sports or NASCAR (I like motorcycle racing), and I'm really bad at small talk.
This makes it tough for me to relate to a lot of people, in that I'm not rude, but if I don't have some common ground with someone, I usually just clam up. It can be a little awkward. As I get older, I find my time more and more valuable, and this personality quirk has become worse in that if I don't feel I have common ground with someone right away, I don't go out of my way to find it. I'm sure this winds up making me look like an a-hole to a lot of people.
I came to this realization through my wifes co-workers. I'm kind of trapped into meeting them through company functions like Christmas parties and weddings. As I go to them and meet people over and over, they get to know me a little and a couple have mentioned I seemed a little uptight at first. I usually just say I'm shy and don't confess to not really caring to meet people without my same whacked common interests. Since I'm aware of it, I can usually drink a couple beers and just try to smile through lots of talk about work, shows I don't watch and sports I don't care about for my wifes sake. She has stayed with me for years, and Peale, I don't think you could really be considered a truly dysfuntional person if you can maintain a relationship with a woman.
I have a buddy who is lots of fun, but he burns through at least one girlfriend a year. It always starts the same "she's different", and I know it's started because he stops calling me for about two months. After that, the calls start back up, and he's suddenly available to hang out at a moments notice because he's sent another broad running!

Maybe your one good buddy just lost his taste for dumpster diving and you're reading to much into it. I can tell you that I wouldn't be into doing that. People change.
I quoted Ray because I disagree with one of his comments. I find sarcasm and self-depricating humor hilarious. I typically find that "talky-smilers" become tiresome real fast, usually because you seem them using the same act on everyone, saying the same things, and it gets old quick. I end up liking someone a bit reserved with a darker sense of humor a lot more. Someone who is cynical, but can be cynical but laugh at the whole thing is awesome.
Edit for horrible grammar.