Of course, in some circles, “take two hits and pass the joint” is as deeply ingrained a rule of politeness as “start with the salad fork” might be in others. But as legal pot becomes more widespread, novel questions arise. Is it an acceptable host gift? Can you consume it in front of your co-workers? What about your kids? Should you bust out a joint at your nephew’s bar mitzvah, or bring out some edibles after your aunt’s funeral?

“They started laughing first,” when she brought the subject up, Pejic said. “And then they said, ‘Wow, this is really new.’ . . . Even [experts in] states where it’s not legal yet, they said, ‘Oh, wow, this is coming.’”

For anyone reared in the “Just Say No” era, the notion of marijuana etiquette might sound funny, even oxymoronic. To many ears, the term “etiquette” has a connotation of rigid propriety. Historically, one function of etiquette has been to enforce social norms, and a legal ban on a substance is a powerful way to prevent the emergence of accepted social manners about how to use it politely.

Yet the deeper purpose of good manners isn’t to show off one’s good breeding or catch other people in unsuspecting breaches of arcane and sometimes arbitrary rules. It’s to help a broad variety of people —- rich and poor, hosts and guests, and, yes, users and non-users of marijuana — navigate complex social situations they encounter in the real world.

And, increasingly, the overt use of marijuana is one of those situations. Massachusetts is one of 10 states that have decriminalized marijuana so far, and the only one on the East Coast to sell marijuana at consumer stores. Since most Americans are supportive of ending marijuana prohibition, Pejic’s colleagues are right — Massachusetts is probably at the crest of a nationwide wave of legalization.