It has taken me a very long time to recognize certain things about the way I was raised to view certain social interactions, a view rooted in the "mind your own goddamn business" ethos of the southwest. It was made clear to me, from a very early age and by most of the adults whose examples I witnessed, that when you had to talk to strangers, the conversations should be as neutral and as brief as possible. You shouldn't be flat-out rude, but you also shouldn't make chit-chat with the guy who takes your order at some bakery/bagel/sandwich chain, because he might then feel it appropriate to tell you, with genuine kindness and your best interest at heart, that the sandwich you just ordered has more calories than any other item on the menu. You shouldn't act like you're actually interested in the thoughts and opinions of the person helping you find a book at some bookstore, because then they might stick around and continue to talk to you when you just want to find your book, buy it, and get the hell out of the store. The only exceptions to this rule are if you are trying to spread the gospel; in that case, you should use these mini-moments of niceness as an opportunity to ask the other person what they know about the Church of Jesus Christ of Latter-day Saints and invite them to church.
Actually maybe that's another reason I used to try to keep conversations with strangers to a minimum: I didn't want to do anything that might invite them to proselytize me. (One more way my religious upbringing screwed up my ability to play well with others.)
But my friend C has no such problem. I have known her for about a year and a half, and hanging out with her has been a revelation, largely because she is so charming, friendly and open: I continue to be astonished at easily she enters into conversations with complete strangers, conversations that, although often very brief, are nonetheless enjoyable to all who participate in and hear them--up to a point.
C used to tend bar. (I so prefer the locution "tend bar" to "be a bartender." It just sounds cooler.) She learned certain things about how to be pleasant enough to people that they wanted to tip her, but not so pleasant that they figured she'd be going home with them at the end of the night. I don't want to make it sound calculated: she has developed a genuine habit of being cheerful, friendly, and polite when she meets people. Which is why the guy at the sandwich shop told her, "That sandwich you just ordered, it's my favorite. I used to eat one almost every day. But then I decided to look it up and see, like, how many calories it has and stuff, and it turns out it's got 1100 calories. It's got more calories than anything else we sell. They're really not good for you."