Such is the power of a 23-year-old, blond former Playmate of the Year in go-go boots. David Letterman could hardly contain himself. “You’re practically naked!” he shouted in the direction of her exposed midriff the other night. “Yo, Dave,” she remembers thinking at the time. “My eyes are up here.”

And beautiful blue eyes they are. But they aren’t what made this Chicago Catholic-girls’-school girl into a pinup fantasy. That would be her–get your mind out of the gutter!–personality. She has one. Jenny makes the rest of the crazed extroverts on MTV look like wallflowers. Hyper and cartoonishly wanton, she plays what she calls her “bunny side” for laughs. On her “Get Next to Jenny” show during spring break, MTV handlers wanted her to lead her hormone-overloaded audience in a chant. “OOH YEAH, BABY,” she was supposed to yell, with accompanying bumps and grinds. She changed it to “MORE WAFFLES, PLEASE,” just to be silly. “I’d rather be a cute, funny person like Meg Ryan than a Pamela Lee sex symbol,” she says. MTV programming exec Lisa Berger “couldn’t wait to hate” Miss 1993, but after seeing McCarthy audition for “Singled Out,” she recruited her on the spot. “She winks at the camera. She doesn’t take it seriously.” MTV does. It’s negotiating a deal to do more with her: a sitcom, a variety show, maybe just all Jenny all the time.

This is McCarthy’s moment. Cybergeeks with handles like Studman and BeerGod have built shrines to her on the Web. She’s in Tom Arnold’s next movie, “The Stupids.” Rolling Stone is about to put her on the cover. Last week Dana Carvey parodied her, a superfluous dig when she so cannily parodies herself. In the “Playmate Data Sheet” that accompanies every centerfold spread, McCarthy declared her ambition “to succeed in TV Land, and eventually get a house, a husband and a Beaver Cleaver family.” Now there’s a sitcom we know David Letterman would watch.