My friend, Kevin, was huffing the other day about a breach of etiquette that he had noticed lately.

Kevin isn’t the fussy type so it wasn’t that he’d spied a lunch companion using the wrong fork or open-mouth coughing at the salad bar.

No, it was far worse than that.

“I just want to know,” he said, “When did it become OK not to thank someone for letting you into traffic? Where’s the friendly wave?”

Where, indeed?

I’d say that at least half the time I let someone into traffic, there’s not even a nod, much less the time-honored smile-and-wave-and exaggerated mouthed “thank you” that used to be the norm.

And while this may not exactly herald the end of civilization as we know it, when coupled with a Donald Trump presidency, it would come pretty close.

Having written an etiquette book that is, at this very moment, on the backs of dozens, if not hundreds, of toilet tanks throughout this great nation, I feel that it’s my duty to weigh in on Kevin’s manners conundrum.

There’s nothing so odious as ingratitude when a stranger does you a solid. If you think about it, this random act of kindness is the purest: you don’t care who’s behind the wheel; you know only that they are going to sit there through a few more cycles of the light if somebody doesn’t let them in.

It’s a true kindness to a stranger because you don’t know them, they can’t do anything for you and you’ve inconvenienced yourself a bit in the process. Particularly if this causes you to just miss the light. Which it will.

Still, you like to do this to remind yourself that you’re not such a bad sort. You may have “put an empty milk carton back in the fridge this morning” or “forged someone’s name on a financial document at the bank” but at least you were kind to a stranger.

“After you, my dear sir or madam.” You’re welcome.

Now there is another phenomenon I have noticed, which Kevin didn’t mention. This happens to me all the time and here’s how it works: You approach the intersection. You see a poor sap in the parking lot to your right and you decide to let him in. You leave a nice amount of pavement for him to pull in front of you and… he doesn’t move.

Just stares at you and sits there. Has he been so sheltered from random niceties his whole life that he doesn’t understand this simple courtesy to a fellow human being?

No, he’s just a dumbass.

So you tap your horn, very lightly, to get his attention. Still nothing. And you pantomime this big, wide, swooping gesture to indicate that he may proceed into the “motorway” as Siri calls it because I haven’t figured out how to make her speak American. Finally, he understands. And pulls in front of you. No wave of “thanks.” Just that Trump for President bumper sticker.

Perfect.