Clinton's spilling! O.J.'S yapping! And we so have an intense urge to throw on some Doc Martens, guzzle Crystal Pepsi, and crank up the Gin Blossoms! Suddenly a bunch of late-20th-century news makers are back in the spotlight, portending the official arrival of '90s nostalgia. While ''neo-alternative'' radio stations like San Diego's KBZT play ''oldies'' by '90s bands Nirvana and Nada Surf, VH1's ''I Love the 90s'' (already!) makes its Tickle Me debut July 12. Just four years into the '00s, why is pop culture eating itself so quickly? One reason is that the MTV demo isn't as interested in what they didn't live through. And the trends were just as fleeting. ''It was a capricious, flippant decade. Styles came and went faster, and trends just don't last as long as they once did,'' says Meredith Ross, exec producer of ''I Love the 90s,'' which will skewer the likes of Amy, Joey, and Tonya. In other words, check back in a few years, Guarini!