If you see a celebrity in a bar or restaurant, what’s the etiquette? Is it OK to ask if he or she is really who you think he/she is? The question came up a few nights ago, when I was sitting at the bar at South Food + Wine Bar in San Francisco. A white-haired, dashing individual sat down beside me. “That’s Richard Branson!” I hissed. My friend wasn’t sure. “Yes, it is!” I whispered, feeling slightly giddy. I needed corroboration. “I’m pretty sure I saw Richard Branson” wouldn’t make much of an anecdote later.

If he was the mogul, he probably didn’t want to be badgered. But he was right next to us, all alone. My friend tapped his arm. “Excuse me. We have an etiquette question for you.” She explained the dilemma: If you see a famous person in a public place, should you let him dine in peace, or is it all right to out him? “You should go for it,” he said. “So can you give us confirmation?” I said. “Yes,” said the ruddy-faced billionaire, looking tickled.

Although Branson seemed to enjoy the attention, he might not have felt the same way if he had been with friends and I’d jumped into his lap and snapped a picture with my cell phone. A couple of days later, I talked to “David,” the husband of a movie star who asked that neither of them be identified. Based on their experiences, David offered a list of dos and don’ts for approaching a celebrity.

DON’T ask for a picture or an autograph. “The reason [asking for autographs] is annoying is most of the time the person isn’t an actual fan, they’re a professional autograph dealer. You’re just signing it so the person can make money.” As for pictures, he says, “You just ate a meal. You might have something in your teeth. And you have no control over what they do with the picture.”

DON’T misidentify the person. David explains, “If someone comes up to you and says, ‘I loved you in The Graduate,’ what are you supposed to say? Like, ‘Thanks, I loved that movie too. But I wasn’t in it.’” Be sure you know whom you’re talking to.

DO choose your moment. “It’s like the Mafia rule: If they’re with family, leave them alone,” says David. “If you see kids, especially little kids, stay away. People come up to you when your stroller’s just collapsed and you’ve spilt milk all over the floor.” And don’t approach in the middle of dinner. Wait until the check is paid. “When they’re putting their coat on, that’s your opportunity.”

DO keep it short. “If the person is a movie star, it’s weird, because you feel like you know them,” says David. “You feel like they’re a friend of yours. You shared something. They cried. You cried. You’re like: ‘We cried together.’” But, says David, “for them this is the 10,000th time they’ve been approached. It’s not the beginning of a friendship.” Don’t hang out and invite them to a barbecue. Say, “Hi, I really like your work,” then move on.

Table Manners appears every Wednesday. Have a Table Manners question? Email Helena.