It’s No. 20 on the Billboard charts and rising. It world-premiered on MTV, along with a ”Making Of” special. It may even inspire its own lingerie line. It’s R&B star Sisqo’s bawdy ”Thong Song” — and not since the days of the itsy-bitsy-teeny-weeny-yellow-polka-dot bikini has such a scanty bit of clothing been glorified so ardently. ”The thong is one thing you can’t deny,” declares Sisqo. Retailers agree. ”We’ve seen our thong sales go up steadily for three years in a row,” says Monica Mitro of Victoria’s Secret. Several merchandisers are wooing the Dru Hill singer to market a ”patented ‘Thong Song’ thong.” Sisqo will also be a host of MTV’s spring break in Cancun — and since thongs are a ”very popular form of beachwear,” says an MTV spokesman, ”our cameras may catch a few people wearing them.” As for Sisqo, who happily shares his fave thong look (”when the cut is in such a way that the girl’s booty looks like a heart”), he steers clear of the wedgie producers himself. ”I wear boxers because I need things to breathe down there,” he says. ”You can’t unleash the dragon if it’s all leashed up.” A little TMI (too much info) — just like the thong.