Well, I was diagnosed with ADD. I've seen a couple therapists, both of whom said I don't have social anxiety disorder, but am introverted. Sometimes I don't pick up on subtle body language and I don't think I'm super expressive (though I'm intelligent and empathic and tend to be liked by people who get to know me), hence the occasional assumption that I'm bored, indifferent, or unhappy. I might be a wallflower occasionally, waiting for a more overt display. People don't think I'm weird, just quiet.
I picked up a copy of Painfully Shy, and the first part seems to be all about sunshine and flowers and donning your superman cape. I'll read it, I don't need a new cape, but it might give good tips on body language and conversation.
In reading the book, I can tell for sure I don't have social anxiety disorder. Though I might be somewhat uncomfortable being alone at a party full of strangers, sometimes I avoid sticking with my friends at parties. I don't think the problem is "fear" or anxiety driven. I just don't see a lot of cues, and if I do sometimes I don't act because I see no reason to. It seems one of the steps isn't developed. Which step is a mystery. As a kid I was made fun of and excluded constantly, so now I'm selfish and overly sarcastic sometimes to the point of offending.