NOW AND THEN, Miss Manners is given to bragging that she never, ever commits a rudeness -- cheerfully undaunted by the fact that bragging itself is rude. But today it is an error of her own, caught by alert and sensitive readers, that prompts her usual lament over what the human race has come to, now that we have scared all the horses off the streets.

The crime of which Miss Manners is guilty is called, by one correspondent, "placism." She made joking references to geographical places of great dignity. Her excuse for making a joke about California is that she didn't know it was a real place; and as for North Dakota, why, her dear father had strictly taught her that it was in bad taste to joke about Fargo, as so many people do, but that Grand Forks, where he had once lived, was fair game. These are poor excuses and she apologizes.

The only truly safe and proper subject for a joke is oneself. Many a person who thought this provilege extended to his or her spouse, parent or child, has lived -- but not very long -- to find otherwise.

It applies to your name, hometown, nationality and so on, but only if this tie is apparent to all. Protesting "But my great-grandmother was half Indian" is not going to change the stony looks that follow your little bigoted joke into great chuckles.

That many connections are not readily apparent is something you can verify by telling a joke making fun of any group that you firmly believe is not represented at a joke-telling. It is a law of nature that someone will respond, in the silence following your punch line, "Perhaps you didn't know that my wife is . . ."

Dirty jokes in unmixed company -- that is to say, jokes that depend on a shared belief in the inferiority of the other sex -- aren't safe any longer, either. It's not only that someone present might be married to a person of the other sex, but that nowadays you can never tell when couples might care more for those with whom they live, than those with whom they share public bathrooms.

Jokes that make fun of the teller's own wealth, ancient lineage or prestigious school or neighborhood are only successful among those who share these handicaps.

Jokes about other people's proper names are never successful. For one thing, the people have all heard every possible one before. You will never manage to satirize anybody's name in a fashion he has not heard since nursery school, and Miss Manners isn't even going to tell you the name of the person who first told her that.

But perhaps for the tradition of the class joke to survive, it is becoming necessary for certain groups to volunteer to serve as the national butt of jokes for a limited term -- as say Cleveland did last year, in kind recognition of Brooklyn and Texas having served longer than their share -- with the promise that another group will then take it over.

And Miss Manners hereby absolves California and North Dakota from service. MISS MANNERS RESPONDS

Q. You wouldn't think that something so common and ordinary as table salt would reqire training to use, but I find myself with several unresolved problems having to do with this seasoning.

1. What is the formal way to serve salt? I am thinking of where it should be put on the table, and in what. Also, how much -- that is, how many salt shakers to a guest?

2. When someone asks me to pass the salt, it is often a reminder that I haven't yet salted my own food. May I do so before passing the salt?

3. If there is a salt and pepper set, do I pass both together, even if only the salt was requested?

A. Common, salt may be, but ordinary, it is not, being truly a seasoning for all men (and women).

1. The really fastidious person will service salt in tiny open dishes, with salt spoons, at a formal dinner, not use a salt shaker. Almost no one except Miss Manners is that fastidious, however. Such salt cellars are placed between every two guests, or, if you want to go all out, one in front of each guest.

2. No, you may not. That is like using a friend's engagement announcement to notice how suitable a partner the betrothed would make for yourself.

3. Keep them together. Like many couples, one is sought after and the other generally ignored, but the polite person will treat them as a couple.

Q. Note a mistake. Samuel Johnson, not Benjamin Franklin, made the comment about fish and guests smelling after three days.

A. Miss Manners begs your pardon. Dear Mr. Franklin not only made the remark, but at least two variations on it; but then, so did nearly everyone else, except possibly dear Dr. Johnson. Miss Manners' usualy cursory research reveals that the witticism was first made by Plautus, in about 200 B.C., and was perfected by John Lyly in 1580, but it was also attributed to half a dozen others. Robert Herrick said it in 1580, for example, and S.G. Champion claims it as a Japanese proverb he unearthed in 1938. Miss Manners herself says it every few weeks. In dear Dr. Johnson's favor, however, let it be noted that he did say everything else.