IF YOU'VE BEEN WONDERING WHAT SCOTT BAIO has been doing since Charles in Charge went off the air in 1990, the answer is, in some ways, just what you'd expect: acting occasionally in movies and on TV and directing numerous sitcom episodes. But what you may find surprising is that, as he approaches his fortieth birthday, the kid from Happy Days is forging a career as a Hollywood Don Juan. To the list that includes Brad Pitt, George Clooney, Kevin Costner and Johnny Depp, now add Baio, the former Joanie Loves Chachi star, who admits he's "not the best-looking guying the world" but whose résumé of beautiful and famous girlfriends is more than a little impressive.
     "It's very simple," says Baio, who stars with Matthew Modine and Ben Gazzara in the upcoming movie Very Mean Men. "I'm on TV, and television has lots of power. Plus, my attitude has always been good."
     Who has loved Chachi? Everybody, it seems. Back in the Fonzie era, he and costar Erin Moran made each others days happy. "That was a hundred years ago," says Baio, who subsequently had a two-year relationship with Spin City star Heather Locklear in the early '80s. "She's a lovely person, a great human being," he says. "I just screwed it up. I became a jerk."
     But not a lonely jerk. In 1989 he hooked up with Pamela Anderson who'd just arrived from her native Canada for her first Playboy layout. "She's no picnic," he says. "In my opinion, she's difficult to deal with." They broke up. But he rebounded with blond siren Nicolette Sheridan. "She's beautiful, smart, funny and tough, tough, tough," he says. "She's a fun human being, but too much work."
     Then there was Denise Richards, the star of the recent James Bond movie The World Is Not Enough. "I met her at a party about three or four years ago," he says. "She's stunning and nice but too goal oriented for me." And Beverly D'Angelo? "The most fun person ever," he says. "She can have a good time in a sewer. But I think she was a tiny bit too old in terms of what I needed."
     To satisfy those needs, Baio started making the Playboy Mansion his home away from home in 1984. "It's like going into a candy store and all your favorite candy is there," he says. "But you have to figure out how to get it." Baio admits he isn't always successful. "I've been turned down many times," he says. "But I lost my ego 15 years ago. This business beats it out of you."
     His advice to would-be Romeos: Attitude is everything. "If you have an attitude like you don't care and you have something to back that up, like money or fame, it's a beautiful thing." For the past six months, Baio has lived with "a wonderful girl from Sweden" who "had no idea who I was when I met her," last July at the Playboy Mansion. Although she isn't a Playmate, she is a friend of Hugh Hefner's secretary. And she is a knockout. "People should know I'm so f----ing lucky," he says. "I'm so lucky you can't imagine."