“I’m going to lunch.”

“Don’t let the dogs loose in the street.”

Everyone wants to create an illusion of the in-joke, the bit of information that only you and they share. When it’s your close friends doing it, that’s easy. When it’s people you’ve just met, the exchange is forced — because they don’t know you beyond the caricature they’ve built in their mind, composed of the few facts which you’ve allowed them to be privy to.

It doesn’t promote a feeling of camraderie to hear someone say “Heard any more kids call you old nekkid guy?” if that’s the only part of your ‘story’ that they know; it just emphasizes how little they know about you.