When screenwriter Cameron Crowe went undercover to observe the species Teenagerus americanus, he returned with more than the usual grab-bag of anecdotes about horny, apple-pie-humping guys and the popularity-obsessed girls who must fight them off with a stick. He returned with 24-karat truth. To watch Fast Times today is to know exactly what it felt like to be fixated on sex, drugs, and rock & roll in Southern California circa 1982. It also launched careers and dished out still-relevant life lessons: Jennifer Jason Leigh (relax your throat muscles when fellating a carrot), Phoebe Cates (always knock before entering a bathroom), and Judge Reinhold (see above). And Sean Penn's Jeff Spicoli, with his checkerboard Vans and bong-hit grin, was a geyser of catchphrases (''Aloha, Mr. Hand!''). The film never strains for coming-of-age treacle. Maybe that's why it still feels so...right. Especially Damone's sage advice: ''When it comes down to making out, whenever possible put on side one of Led Zeppelin IV.''