YOU KNOW IT'S SUMMER IN WASHINGTON when you are standing at the Metro ticket machine, surrounded by a great noisy clot of your own relatives and their friends and assorted hangers-on, and you, who feel responsible for these people's safe passage into the city, are patiently and rather pedantically trying to show your own father how to use the Metro ticket machine, and truth be told you are having a hard time even though you use the Metro nearly every morning of your life, because your dollar bill is crumpled and those new ticket machines are hard to get used to, with their confusing multicolored buttons and slots, the most obvious of which, it seems, are never the ones you're supposed to push.

"Try pushing that little white triangle beside C!" I'm telling my dad, fishing out the extra cash needed to get him a round-trip ticket and purchase round-trip tickets for the other members of our party, which includes my own two small children, sitting together in a Titanic-size double stroller.

You know it's summer in Washington when a line begins to form behind you, a line full of impatient natives who need to get to work, and out of the blue one of them, an elderly man, comes up and offers, helpfully: "Get a round-trip ticket! It will be easier that way!"

And you turn around and realize that he's not talking to your dad. He's not talking to the assorted hangers-on.

He is talking, quite clearly, to you.

You know it's summer in Washington when a total stranger mistakes you, a longtime Washington resident, for a tourist. Just because it's your day off and you're wearing shorts and carrying a backpack and have your children in a Ford Expedition-size stroller and are having trouble getting the Metro machine to take your crumpled dollar!

"I am getting round-trip tickets," I point out, coldly. "I live here!"

You know it's summer in Washington when you hear the train coming and you and your big party of embarrassingly lost-looking relatives and their friends and assorted hangers-on, clutching their round-trip tickets and trying to figure out where to stow them, rush onto the escalator, stream through the train doors an instant before they close and then, with much fanfare and laughter and self-congratulation, sit in a big mass that takes up half the car.

"I highly recommend the National Gallery of Art!"

Holy traffic pileup! You know it's summer in Washington when the old man has nimbly managed to follow you onto the train to offer a bit more advice!

"I know," I say. "The National Gallery of Art is where we're going."

"And bring your children!" he continues. "There's nothing wrong with taking children to museums. They have strollers there, and elevators. That's what I always tell tourists -- bring your children!"

"I have brought my children," I say. "And I'm not a tourist!"

"The only three places in Washington I don't recommend to tourists," he continues, "are the Bureau of Engraving, the FBI and the Air and Space Museum, because they're all part of TV trash culture. There are so many other, better places to visit. For example, you can go to the greatest Shakespeare library in the world! Do you know what that is?"

"The Folger Shakespeare Library," I say.

"The Folger Shakespeare Library!" he says. "Moreover, there is a wonderful new memorial down by the waterfront, the . . ."

"FDR Memorial," I say.

"FDR Memorial!" he says. "I had the privilege of voting for him in his last election. Do you know, how did your grandparents feel about Roosevelt?"

You know it's summer in Washington when you realize that this man is never, ever going to accept the fact that you're not a tourist. And meanwhile your own father, sitting behind, highly amused because this person thinks you, a longtime resident, don't know anything about the place where you live, begins to play along.

"I don't think her paternal grandparents liked Roosevelt," my father interjects. "But her maternal grandfather liked him very much."

"I had the privilege of voting for him!" hollers the old man.

"Really!" my dad hollers. "You don't look that old!"

"I'm 77!" the man says proudly.

"I'm 72!" says my dad, who is 64, and then my dad starts talking about how he landed at Guadalcanal, which is a bunch of horse doodle. And by now it's hard for me to tell who is worse, in Washington, in the summer: the natives or the tourists.

You know it's summer in Washington when finally you, a longtime resident, aware that the whole Metro car is watching, and laughing, sit back and with assorted members of your party begin making loud, obnoxious jokes about the name "Foggy Bottom," accepting your designated role as hinterland doofus and figuring what the heck; it is, after all, summer in Washington.

Liza Mundy's e-mail address is mundyl@washpost.com.