I wasn't born with a naturally perky, outgoing personality. I'm not shy; I like people fine; I'm just not chatty unless I know someone fairly well, and sometimes not even then. The up side of this is that people confide in me because I'm a good listener. The down side is that a lot of them have said, "Wow, when we first met, I thought you totally hated me!"
(Did I slash your tires? Spit at your feet? Eye you meaningfully while spraying myself with Eau de Loathing cologne? No? Then I probably didn't hate you.)
Because I've been told this so many times, after an ordinary interaction like the passing chat I had with a neighbor yesterday evening, I walk away all paranoid, thinking "Did I seem friendly/happy/enthusiastic enough? Did I end the conversation too soon? Shit, did I forget to smile? I'll bet I forgot to smile. Great! Now they think I hate them. They're going to point out my house to visitors and say, 'That's where the witch lives.'"
Long story short, if you meet someone who's not bubbling over with small talk, please don't think they're snobs or jerks or that they wish you would die in a fire. They're probably just like me and will talk when they have something to say.