Say your friend posts a photo online of the gorgeous house she just bought. You want to be happy for her, but you can’t stop thinking about how you’re trying to make ends meet in your small rental.

When Dr. Priya Mistry asks people if they clench their jaws, they usually say no—yet she can see clear signs suggesting otherwise. So now, she words the question differently: Are they aware of their ...

There’s complaining. And then there’s complaining. In its more benign form, complaining between friends can feel beneficial. Light grousing about a mutual foe, for example, can cultivate camaraderie.