How I wish that the world of commerce always made sense. Sometimes it seems to make very little.

Jack Mueller of Springfield is a head-scratching case in point. Jack attends mass each morning at St. Michael's Catholic Church in Annandale. Afterwards, he and some friends often go to breakfast at a nearby Big Boy restaurant.

One day in December, Jack decided he didn't want a whole cup of coffee. So he asked the waitress to sell him a half a cup of coffee rather than a whole cup.

The waitress refused, and the manager backed her up. "They said they couldn't do that," Jack writes. When he asked why, the manager replied, "Because that's the way coffee comes."

Big Boy gives free full-cup refills till the cows come home. But Big Boy won't give a customer the half cup of coffee he wants -- and is willing to pay for. Hmmmmmmmm.

Asked to comment, Leslie Schlags, a corporate relations supervisor for the Marriott Corp., said this:

"There's no way to measure exactly half a cup. If we gave him half a cup, then we'll get people who want two-thirds of a cup. It's important to maintain standards . . . .

"Marriott has always tried to be responsive to customer demand. But there's no good procedure in this case for being sure we don't gyp somebody. I don't want to say there are some things we can't do, but . . . .

"The best analogy I can give you is that you can't go into the grocery store and buy half an apple."

I greatly doubt that a customer is going to come to Big Boy with a set of calibrated test tubes to make sure he's getting every ounce of the half cup of coffee he has paid for.

And I don't see what's so awful about a guy asking for two-thirds of a cup. If you can measure two-thirds of a cup in your kitchen, you can certainly do it in a Big Boy restaurant.

But it's not just Big Boy that won't bend when the customer says bend. It's also an ice cream store in Rockville called Sweeterie.

Marion F. Wolff of Bethesda says she strolled in one day and asked for "the smallest amount of mocha ice cream." That was in case her Guilt Affliction Center was listening.

According to Marion, the clerk put one scoop of mocha into a cone. She was about to plop a second on top of the first when Marion said, "I just want a single scoop."

"Our singles are double scoops," Marion says the clerk replied.

"In that case," said Marion, "give me half a single." The clerk obliged. But she charged Marion the same as she would have charged for two scoops.

Owner Emily Bressler was puzzled by the story, because Sweeterie sells ice cream cones in 4-ounce and 7-ounce sizes, not by the scoop.

Is it possible a four-ounce mocha cone would consist of two scoops? "It depends on the scooper, and who's doing the scooping," Emily said. She added that she is "concerned about the confusion."

That makes three of us.

I trundled up to 17th and L streets NW the other night just as an ambulance was trying to go north on 17th, against the light.

The driver stopped before entering the intersection, just as "the book" says he should. He turned his siren and emergency lights on full blast. He even glared in the direction of the L Street traffic so that the drivers in the front rank would know he meant business.

Three cars went right through the intersection as if the ambulance weren't even there.

One of the three drivers even waved thanks to the ambulance for letting him pass.

How dangerous is this? Extremely. Who lives with this problem every day? All of us. But perhaps the most threatened collection of humanhood is the ambulance drivers and their families.

One member of that latter group is Sherri Stebbins of Alexandria. Her husband David is a paramedic for the Arlington County Fire Department. Sherri hears constantly from David about Siren Scofflaws. She asks that I tell the world the following:

"Those who still continue to show disregard for emergency vehicles could keep in mind that they may yet meet my husband. While he stands over them doing the job he does so well."

Thanks, Meredith G. Williams of Potomac, for this goodie.

A woman wrote into a Bridgewater, Mass., newspaper advice columnist about her 85-year-old father. Seems the old boy had been singing hymns and reading the Bible constantly. The woman was worried that her father was slipping mentally.

Wrote the advice-giver: "He is probably only studying for his final exam."