Why do people do it?

Now that I am working, and you will hear me say that a lot, I hear some of the weirdest things that people say when they think your not listening. Just because I'm ringing up the stuff that your buying doesn't mean that I'm listening to you, so you might want to be careful who and what your talking about, like your sex life. I don't want to hear about someone that you had sex with,where you did it, and how many times, gross!! Yes I've had sex, hence the daughter that I have no, but still I don't need the graphic details of your last sex session.
In that same line of thought feel kinda bad for the guys that come thru my line buying condoms. I wonder are they embarrassed when they come thru my line, is that why they don't make small talk like every other person that does? Or are they just in a hurry and have some hot chick waiting for them at home/hotel/car? lol. I love it. It's just funny.