Chalk up one more thing your parents told you not to do that could be good for you after all.

Swearing. Cussing. Cursing.

The expletive exploding from your mouth when you bump a shin, topple a full coffee cup or are cut off by a maniac driver in rush-hour traffic.

"----," you yelp. "Oh, ---- ---- ----."

It helps.

"Profanity, swearing or whatever you want to call it," says Chaytor D. Mason, a clinical psychologist at the University of Southern California who has made something of a hobby out of the subject, "is a time-tested and effective method of releasing emotions built up by frustration.

"You tense your muscles and let go."

To release tension, the shorter the word, the better--which is why so many have only four letters. "With a more complicated word, you're not really letting go."

Sexual, scatological or biblical, says Mason, it doesn't make much difference which word you use so long as it expresses raw emotion, breaks through social restraints and is not overdone.

"When a person is frustrated," says Mason, "he or she really wants to destroy. The purpose of swearing is--at that moment--to become anti-society, to ripple the emotional muscles."

"Darn," "Shoot" or "Oh, shucks" aren't the same.

Swearing is particularly useful today, claims Mason, "because problems now seem to be more complex and therefore more frustrating than ever before." It's far more prevalent--and accepted--in such high-stress jobs as politics, aviation and construction.

But because profanity is still frowned on in some circles, he advises refraining until you develop a certain rapport with, for example, "a boss, an academic review board, a radio audience."

The urge to cuss, he says--"I swore at a very young age"--probably has been with us since the dawn of civilization. Cavemen and women may have uttered "profane grunts" or at least used profane gestures, a practice also surviving the ages. He quotes Freud as saying civilization really began when (in Mason's words) "instead of chopping off someone's head, you cussed him."

"To my knowledge, all languages have cuss words," he says, though he has heard that the inhabitants of a Melanesian Island may be so happy they haven't needed any. But generally, profanity is "rampant . . . There are darn few people who don't use it."

Our country's Founding Fathers had cursers among them, Benjamin Franklin among the lustiest. "But the average school gives a picture of a plastic saint. Educators should begin admitting to students that many of our historical heroes were people who swore like the dickens.

"I think we ought to know that. I'm delighted to read about Jack Kennedy's sex life. And Jimmy Carter, when he said in the Playboy interview he had lust in his heart, become more human. He wasn't the choirboy that flacks painted him."

From Watergate we learned that Richard Nixon was far more profane than he had let on publicly. Far from finding the language offensive, "It reassured me."

The language of diplomacy is "very unprofane. Their words are so guarded our adversary doesn't understand the depth of our feelings. If we were more directly profane, the Russians might get the idea we are more serious."

The State Department, for example, typically phrases warnings in such terms as, "We are not going to tolerate that incursion into the European scene."

How much more effective, blurts Mason, to be blunt: "Get your a-- out!"

And swearing can be a gesture of camaraderie. As a former Marine, he knows military buddies are more apt to call each other "lousy S.O.Bs" than "good fellows."

After all that, he does concede that swearing, like anything else, can be overdone. "People who swear all of the time may be emotional volcanoes in danger of erupting." Among the young, it may be "rebelliousness. They've known the words since they were 4 or 5. This comes out as a way of testing the self."

On the other hand, people who never utter a swear word "could be a potential Mt. St. Helens." Such people, he says, are often "afraid of other people, afraid of what other people will think."

Mason's primary work is in aviation psychology at USC's Institute of Safety and Systems Management, for which he travels the world lecturing pilots and flight personnel on air safety. His experience as a frequent "expert witness" in plane crash investigations has stimulated his interest in swearing.

"Pilots under stress cuss. Cockpit voice recordings are full of cuss words (often deleted, to his chagrin). Typically, a pilot will say 'Oh, s---' before hitting the ground. What people do under stress is indicative of their personality."

Had the pilot exclaimed "God help me," it would, he claims, "be indicative of a dependent type. Dependent persons are out of their depth more readily." On the other hand, if the pilot's expletive was something shorter and stronger, it would suggest "a more independent type, but one who has run out of ideas or ways of handling" the crisis.

Americans are swearing more these days, believes Mason, "because we're becoming more realistic" as we gradually emerge from the Victorian age. And society appears more accepting, judging from movies and television. "I think that's a healthy sign."

The big upsurge came, he says, just before and during World War II, when millions of men (and women) were introduced to foul barracks language. Novelists began putting cuss words in the mouths of their heroes. "It showed us that we weren't really that odd."

When Mason began speaking on the subject of profanity, a USC executive thanked him for helping him overcome a longtime guilt about swearing.

"Psychology," he says, "is reassuring people that they aren't so bad. I think you'll find more and more women swearing as they occupy roles that traditionally were dominated by men. It's very important that women do swear. They have the same depths of emotion as men and less ways to deal with it. As women are truly liberated and seen as equal humans, they will swear."

He even suggests that women may have switched from fainting to swearing as a release of stress.

Still unconvinced about the impact of cuss words?

Consider "Gone With the Wind," says Mason, in which Rhett Butler showed "his absolute and complete contempt" of Scarlett with his famous " 'Frankly, my dear, I don't give a damn.' "

And then consider: "'Frankly, my dear, I don't really care.' "