John Yiallouros says he "didn't have any reason to do it. It's just a hobby. I had a dollar in my hand one day and, you know . . . ."

You certainly do know, because the ceiling of the Greek Boy Restaurant in Rockville tells you.

Stuck into the square, white acoustic tiles over your head are dollar bills. Hundreds of dollar bills. Dollar bills rolled into the shape of rocket ships. Dollar bills hanging down over John Yiallouros' restaurant like so many watchful green stalactites.

"How do I do it?" repeats John Yiallouros, as if he has answered this silly question a million times. "I show you how I do it."

John takes a dollar and rounds it into the shape of an ice cream cone. Then he folds the cone flat. Then he folds it flat again. By this time, the bill has a point that would make a mosquito jealous.

John holds the bill gently between his thumbs and forefingers. He turns his palms out, as if he is preparing to make a chest pass in basketball. Suddenly, he aims at the heavens and pushes away sharply. Whip! Smack! Another bill is sticking to the ceiling.

Greek Boy is not the kind of restaurant that will give Lion D'Or a run for its money. It's the kind of place where guys in uniforms stroll in and order six cold Buds to go.

The counters are worn with age. A sign on the back wall says, "I'M 40 AND DAMN PROUD OF IT." The most expensive special of the day is meat loaf and two vegetables for $3.95.

But there is nothing economy-priced about Greek Boy when it comes to Children's Hospital.

For the last six months, the gang at Greek Boy has been collecting "ceiling money" for the hospital that I try to help each holiday season. Last Friday was the day John decided to take it down, count it and donate it.

No one knew exactly how much was up there. Guesses had ranged from $325 to $500. Greek Boy regulars admitted that beers -- many beers -- had been wagered on the final figure.

Most of the money had been donated by Greek Boy customers. They had been prodded by the bright red sign that's glued to the facing edge of the cash register. It reads:

"LOOK UP! ALL THE MONEY STUCK IN THE CEILING WILL BE DONATED TO CHILDREN'S HOSPITAL."

Why Children's? "A guy came in one day. His kid had been there, and he was satisfied with it," said John, who has owned and operated the restaurant for 15 years and who has four children between the ages of two and nine.

The luncheon crush was thinning out a bit, so a counterman went into the back to find a squeegee mounted on a ten-foot pole. A customer in a booth claimed to have seen the implement before.

"He uses it to stir the potatoes," the customer said. In mock retaliation, waitress Debbie Walters aimed a forehand at him with a menu. Greek Boy is that kind of place.

John Yiallouros and the counterman took turns swatting dollars loose from the ceiling. As they fell to the floor, two waitresses, the cook, a customer and a columnist retrieved them. It took us the better part of an hour to flatten and count all that money. But the final tally of $347 made the hour well worth it.

"Now the flies will have no place to sit," John Yiallouros joked. But as a columnist pointed out, the flies' loss will be sick kids' gain.

From the Children's mailbag . . . .

Laura Cramer of Fort Meade began her letter by righting an imbalance. "It seems as if only adults write to you," she said. "I'd like you to know that you have a 17-year-old fan, too!"

Being more than a quarter of a century beyond 17, that sounded pretty good. But what followed sounded even better.

"I am also a big fan of my Dad, whose 47th birthday is tomorrow (Dec. 11)," Laura wrote.

"I saved some money from my Christmas funds to buy him a gift. But when I asked him what he wanted, he said, 'Nothing, really. I have everything I need.'

"It was last night, as my religion class discussed how hard it is for one person to make any real difference in the huge problems of the world, that I decided to try, despite my 'insignificance.'

"Happy Birthday, Dad! And Merry Christmas to Children's Hospital!" Beneath which was a $20 check.

I'd say some 17-year-olds have their heads glued on pretty straight, wouldn't you?

Meanwhile, Audrey S. Koch of Rockville proves once again that there's nothing like a satisfied customer.

"When our middle daughter, Deborah, was six years old, her appendix burst," Audrey writes. "She was very, very sick, and Children's Hospital took wonderful care of her.

"She is now 33 and is spending a year at grad school at Harvard, so this is our 27th check."

That makes you one of our longest-running contributors, Audrey. Welcome aboard once again.

As for the rest of you satisfied Children's customers, how about a contribution, for the former patient in your life?

Here are the latest members of the group givers' honor roll:

AMS, F & V, U.S. Department of Agriculture ($200).

Gallaudet University Alumni Duplicate Bridge Gang ($23).

Penny Riley's 3B class at The Langley School in McLean ($115).

The Military Aides to The President ($100).

Unit 721C at the Veterans Administration ($50.15).

Mrs. Skolaski's sixth-grade class at Brandywine Elementary School in Brandywine ($35).

Players and fans, Federal Aviation Administration Coed Softball League ($70).

The Section Six Bay Hills Bridge Club ($42).

Capital Chapter, National Association of Retired Postal Inspectors ($50).

Administration Department, Investment Company Institute ($65 in lieu of exchanging gifts).

Staff, Citicorp Real Estate Inc. ($200).

Staffers in the Publishing Division, Directorate of Information Management and Administration, U.S. Air Force ($40 in honor of Penelope Paras).

Ninth Floor Employes, Income Maintenance Administration, D.C. Department of Human Services ($52).

Funseekers Bowling Team from the AFIN/ASIS Mixed Doubles Bowling League at Fort Belvoir ($35 in honor of Ellen and Raymond Graves and Bernie and Dick Shear).

Aurora Hills Recreation Center Duplicate Bridge Players ($100).

Lutheran Laymen's League at Mount Olivet Church in Northwest ($25).

Correspondence Unit, Office of Congressional and Public Affairs, FBI ($535 from an annual hot dog and bake sale).

Employes of the Paper Procurement Section at the Government Printing Office ($91).

Centralized Operations Group, C & P Telephone Company ($237 from a turkey raffle).

Class 5B at The Langley School in McLean ($122.81 from a doughnut sale, with special thanks to 5B class president Jacob Gerli).

Lake Jackson Lions Club of Manassas ($100).

TO CONTRIBUTE TO THE CAMPAIGN:

Make a check or money order payable to Children's Hospital and mail it to Bob Levey, The Washington Post, Washington, D.C., 20071.