They’re Talkin’ the Talk : Slang-punctuated chatter is nothing new for teen-agers, but it’s continually evolving.

In 1964, Denny Thompson walked into his father’s store after his first day at Valley College and announced that school was “bitchin’.”

“My father quickly introduced me to the parking lot,” Thompson says. “He thought I was using a dirty word, and all I was doing was repeating what I heard in school.”

Now Thompson is assistant principal for counseling at Chatsworth High School and he’s trying to keep up with the slang of today: “It’s hard to understand sometimes. Bad means good, fresh is used a lot now, and mad-dogging is giving someone a dirty look.”

While parents may be disturbed by such baffling speech, Thompson and other observers of youthful culture see it as a necessary part of fitting in and of establishing independence--as long as it doesn’t go too far. On his strolls through campus, Thompson regularly tries to pick up on what his students are saying.

“A guy can be fresh , and that’s good; that means he looks fine,” said Carolina Federovsky, 18, of Canoga Park.

“A girl can diss a guy and that means to shine them on,” says Fernando Santiago, 18, of Canoga Park.

Neither Santiago nor Federovsky talk that talk at home--Santiago because his family speaks Spanish, Federovsky because she doesn’t want to be impolite. On the other hand, Tami Turner, 16, of Granada Hills, says: “Sometimes my expressions do creep in when I talk to my parents, but I try to watch it. There’s a lot of phrases that we say now that you can’t even print in the newspaper.”

At one time, students could be expelled from school for using a four-letter word. These days, Thompson hears such words all the time from students. He tells offenders that certain words are unacceptable, no matter whom they’re directed at. Students tell him to chill .

In Van Nuys, Daniel Gruenberg, Grant High School’s dean of students, says he has to be careful about correcting some speech. “Kids are always being corrected,” he points out, “and sometimes they’re corrected incorrectly. Someone should point out really bad grammar, but trying to alter slang is like changing their dress or hairstyle.”

When his own 18-year-old called him homey , it rankled Gruenberg, but he tried to understand what the word meant. He adds that he likes to know what young people are saying, but he’s cautious about using their expressions himself. “Otherwise,” he says, “you come off as patronizing. You don’t want to lose their respect.”

For two years, John White has compiled some of the expressions he’s heard as an assistant principal at Sherman Oaks Center for Enriched Students. While he finds the slang fascinating, he encourages students to reach for creative substitutions for downright offensive language. “They’ll go around saying ‘Kiss my derriere,’ ” he says, amused, “or ‘You ugly face,’ or some . . . hilarious similes.”

The danger of using colloquialisms unthinkingly, White believes, is that they tend to creep into inappropriate contexts. Such talk should be restricted to one’s group of friends, and not be used in classrooms, at work or with adults, White says.

What amuses Thompson is seeing some expressions from his own past cropping up in the language of today’s youth: “Sometimes I’ll hear something and realize that my dad tried to get me to stop saying that. And I’ll think, ‘Hey, that’s cool, man!’ ”

From the Mouths of . . .

Here’s a list of some of the latest schoolyard babble (jargon) compiled from students and administrators at Valley schools:

accessorize: to add to, especially as in boyfriends; i.e: “She’s into accessorizing her social life.” -age: a suffix added to just about any word for emphasis or hipness; i.e.: moppage (hair). aks: instead of ask; once solely Afro-American, now widespread. babes: good-looking guys; NEVER girls. bagging on: telling someone’s secret, saying something negative. Betty: a girl with loose morals. bite it: to leave, to wipeout, to die. bush: marijuana. del lingo: expressions of speech, colloquialisms. de-ment: (pronounced DEE-ment) an unpredictable nerd. dope: (adjective) great, cool. edged: ticked off, nervous. goof: tease, play a trick on, tell a white lie. H-and-G: hello and goodby. hummer: a student who just barely gets by. jagging: cruising in a car. kicking it: hanging out, lounging. leperful: adjective describing a person to avoid. Lisa: the girl of a guy’s dreams. magnatron: a girl who turns guys’ heads. mall doll: a girl who spends her time at the mall. Male version: mall troll. Mark: a stepfather. shredding: (adjective) terrific. snake out: check out, look. squab: a disagreement. surrender to hormones: to engage in too much sex. tattered: dressed to impress. twigging: getting it, understanding; i.e.: “After referring to this list, you may start twigging your teen-agers.”