All Fools' Day. You can't say it has the class of, for instance, All Saints' Day. It's not even a holiday.

But for many the day is something special. Just the name of it conjures up visions of raw liver in people's beds and rubber mice in their shoes.

Let's face it. Some people are more disposed towards the day than others. Maybe it's for reasons of heredity, or upbringing, or having been seated too near a radiator while the brain was in a critical growth phase.

Still, whether prepared for it or not, most everybody wants to get into the act on April Fools' Day. And they should. It brings to mind the old French axiom, "Ou est la salle de bain--mon fre re est une poisson," which translates roughly as, "There is always room for one more, though don't ask to borrow the car."

The origin of April Fools' Day--although it is said to have come out of 18th-century England--remains a mystery. One authority dates the event back to the Duchy of Westphalia in 15th-century Prussia, but there is now evidence he made this up to impress his secretary.

But what does it matter how the day evolved? Who cares where a dollar was minted, just so you can spend it.

The basic element of April Fools' Day is the prank. For our purposes here, a good definition is a good-natured trick that plays gently upon the foibles of our comrades and friends. If it also happens to make things hot for someone we abhor, so much the better.

As with everything in life, there are limits to how far a prank should go. A general rule of thumb would be to err on the side of understatement. Put another way, hesitate before doing anything likely to result in the appearance of a large number of uniformed men carrying weapons. And don't humiliate anyone who is the difference between you enjoying expense-account lunches and begging strangers on the street for spare breath mints.

A few ideas (and don't forget to say "April Fool!"):

When your spouse kisses you as you arrive home, say, "Knock it off--I get enough of this at the office."

Have the restaurant chef called out and ask him since when were charcoal briquettes classified as a food item.

Turn to the person sitting next to you on the crowded subway and say, "Oh, no. I should have sat facing the other way. I always throw up when I ride backwards."