If you ever listened carefully to people talking in real life, you know real people almost never speak as well as the fake people in books.
Real people ummmm, and errrrr, and repeat themselves constantly. They talk around themselves, say inconsequential things, break in on their own lines of thought. It's a mess.
Book dialogue, even when it's colloquial, is always more formal, grammatically better, and doesn't say the same thing three times in four sentences.
But every now and then, I hear something that would make perfect book dialogue. Today at my local coffee shop, a girl in her early twenties was making the coffee. When a waitress called the coffee server Jenny, the guy behind me, obviously a regular and about the same age as the girl, started the following conversation:
Guy: “Jenny. Is that your name? I didn’t know.”
Girl: “Yes, it is. You only had to ask.”
Guy: “I couldn’t, you make me nervous.”
Girl: “Oh! Well you make me nervous too. We better get married then.”
Guy: “Yes, and have lots of nervous children.”
Neither of them missed a beat. I swear it was exactly as I wrote it. You know this little dialogue is going into one of my books, don't you? I would have told them that, except at this stage the girl making the coffee had turned a bright, bright red.
I'll update you on any impending nuptials.