According to this piece in the New York Times, talking to strangers is good for you, partly because you tend to act happier around strangers than you might feel.
When one of us, Liz, was in graduate school, she noticed that her boyfriend, Benjamin, felt free to act grumpy around her. But if he was forced to interact with a stranger or acquaintance, he would perk right up. Then his own pleasant behavior would often erase his bad mood.
One of the perks of being a behavioral scientist is that when your partner does something annoying, you can bring dozens of couples into the laboratory and get to the bottom of it. When Liz tested her hypothesis in a lab experiment, she discovered that most people showed the “Benjamin Effect”: They acted more cheerful around someone they had just met than around their own romantic partner, leaving them happier than they expected.