Reading Susan’s post here, I was reminded of my grandfather. Grandpa gave most of his advice with his actions, but he once told me, “Don’t marry a man who is mean to the waitress.”

Grandpa was bit of a flirt with the wait staff. Didn’t matter if we were just going out for $2 burgers, he always acted like they’d made his day by bringing him his food. They’d come by, ask how things were, and he’d always say the same thing: “The quality of the food was only exceeded by the charming service.” Sometimes they’d give him a look like maybe he was messing with them, but then the toughest chain-smoking tight-permed truck-stop-counter hardass would have to smile, because this five-foot-ten elderly fellow with soda-bottle glasses and big thick hearing aids and ears like a cab going down the street with the doors open would be grinning the most infectious grin you ever saw on a human being and there’s no way he was having them on. He meant it. And he always left them something extra, too.

That advice he gave wasn’t exactly what we always hear, right? It’s usually “marry a man who’s nice to his mother.” But plenty of assholes are nice to their mothers. Serial killers are nice to their mothers. Grandpa’s point was that the true test of someone’s decency is how he treats those who he could abuse with impunity if he so chose. The waitress depends on you for her livelihood, for her job, and lots of people with power issues find it easy to take them out on people like that. You’ve all seen it, in stores or in restaurants or in your jobs: Somebody picking on the weaker person just because they can.

Somebody who has to remind the help that they’re the help will, sooner or later, treat everybody in his life that way. Somebody who needs to kick those beneath him to prove he’s a big man, publicly and unnecessarily, will eventually do that to you, once you become inconvenient. Somebody with creepy power issues and problems with his manhood is not somebody who needs a girlfriend, and sending a steak back four times and then berating the person who brings it in front of his or her manager is a pretty big flashing light that says RUN RUN RUN.

For what it’s worth, I followed Grandpa’s advice. He and Mr. A got on famously from the minute they met until the day Grandpa died, and I must have passed along his words a hundred times.

What’s the best relationship advice you’ve ever gotten?

A.