This year's April Fool joke is on every taxpayer in the District of Columbia who earns less than $50,000 a year.

Come April 15, they'll be paying a dollar or two in extra taxes because the D.C. government decided to make it easier for them to figure their income taxes.

Instead of calculating the amount of taxes due from rate schedules, everybody with a taxable income of less than $50,000 can use tax tables this year.

The catch, lawyer J. E. McNeil points out, is that the tables result in most people paying slightly more than if they calculated their taxes directly from the rates.

McNeil says that in figuring taxes for her clients, most of them wind up paying $1 or $2 more based on the tax tables than they would if they used tax rate charts and a calculator.

Someone with a taxable income of $3,503 would owe the District $116 according to the table versus $115.18 (which can be rounded off to $115) calculating the taxes. On a taxable income of $13,558, it's $842 from the table versus $840; on a $27,355 taxable income, $2,211 versus $2,209. Until this year all D.C. taxpayers earning more than $5,000 figured their taxes from rate charts, right to the penny. This year there are tables running up to $50,000. And you must use the tables.

There's no suggestion the District is deliberately dipping into taxpayers' pockets; it's just the effect of setting up tables with taxes for a range of incomes rather than figuring each to the dollar.

"It's only a dollar or two," says McNeil, "but a buck is a buck, and they're collecting an awful lot of extra money from the people who need it most."

While the Postmaster General of the United States was floating over Washington in a hot air balloon last week, I was getting hot under the collar about the mail service he manages.

Everybody has horror stories about the Postal Service and ordinarily I figure my personal misadventures are no more newsworthy than those of anybody else.

But when I saw the pearly white teeth of William F. Bolger grinning out of a publicity balloon blown up by magazine millionaire Malcolm Forbes, it was too much.

On the day that the postmaster general decided to go ballooning, the post office was for the fourth time in a row delivering the same letter to the wrong address. My address.

The first time this persistant if misguided missive arrived addressed to someone I'd never heard of, I did what I consider my duty. I wrote "not at this address" on the front of the envelope and dropped it back in the corner mail box. hen the same letter showed up again, a couple of days later, I added the note "return to sender," underlined the original rejection and returned the letter to a box.

Three days later, it came back again.

This time, the message to the mailman got nastier and the ink got as red as my face: "Mr. Postman, can you read? Please don't deliver this to me again."

What you see above could be interpreted as evidence that literacy is indeed no longer a requirement for letter sorters. Unfortunately I cannot accept such a logical explaination; I'm sure the truth is much more bizarre.

But I really don't want to know. I don't care WHY the post office does what it does. If the postmaster general wants to go up in a balloon to sell $10 stamps, let him.

But when he comes down, he's gonna have to figure out what to do about this letter. Now, I've finally found a way to assure it is not delivered to me again. Today, I'm sending it back to the Post Master General. And to be sure he gets it, I'm sending it by Federal Express.

Finally, a little more bad news before we get to the good.

If there was ever any doubt about the adage that the customer is always right, it was put to rest for ever by the owner of the Georgetown liquor store that journalist Carl Leubsdorf has been patronizing for as long as he's lived in the neighborhood.

It all began when Leubsdorf, bureau chief for the Dallas Morning News, called up to order a case of wine, came in to pick it up and found not only that the wine wasn't there as promised, but that the friendly wine merchant he'd been dealing with for years had flown the coup.

The new bird told him the moderate-priced wine he'd wanted was also gone for good and persuaded him the only alternative was a brand that cost $3 a bottle more.

When in the store a week later, Leubsdorf found his favorite brand was not only in stock, but at the same old price. An inquiry degenerated into an argument with the new wine specialist, prompting a request to talk with the manager.

The manager's warning that, "I'm busy, I've only got three minutes," was a clue that the customer was in trouble. The suggestion that the new wine expert was neither as polite nor as professional as his predecessor and had alienated a long-time customer was rebuffed in classic style:

"I'm not concerned," replied the store manager. "Wine sales are way up since we hired him, and good help is a lot harder to find than good customers."

Such horror stories are all too frequent evidence that some businesses succeed despite doing nearly every thing wrong.

But an amazing number of businesses not only are run right, they work better than customers ever expect. A friend with an auto accident claim that was a potential hassle came away from Geico's drive-in claims service totally impressed. In less than an hour, without even a maybe, he got a check for repairs and a rental car. ervice above and beyond the norm is recognized too infrequently, so for the next few weeks, I'd like to collect annecdotes about people who do their jobs right--the true professionals of Washington business.

Whether its a Geico claims adjuster who restores your faith in insurance companies, a cop who rescues your cat or a clerk who proves bureaucracies don't have to bungle, let me know.

I've heard enough of rudeness, crudeness and incompetence, tell me some good news. Nominate the best of Washington's business people, the unheralded superstars who really try to make things work. If you've dealt with a genuine pro, a Washington business superstar, write a brief nominating note to: Monday Morning, Washington Business, The Washington Post, 1150 15th St. NW, Washington, D.C., 20071.