Joe Piscopo -- who plays Danny Vermin, principal bad guy in 20th Century Fox's 1930s gangster spoof "Johnny Dangerously" -- is not a bad guy in real life. In real life, he's just a guy. From Jersey.

And unlike most TV personalities born in Passaic, N.J. and about to make their feature film debut, Piscopo still lives in the Garden State -- maybe 15 miles away, as the refinery smoke flies. This makes modesty possible. In Piscopo's case, it makes modesty a way of life.

"Y'know, I feel funny taking credit for being a part of this movie," says the generally soft- spoken Piscopo, possibly best known for his deadeye impersonations (of such as Frank Sinatra, Andy Rooney, Jerry Lewis, lightweight one-word sportscasters and, well, guys from New Jersey) during his three years in the cast of NBC's "Saturday Night Live."

"It's really Michael Keaton's movie, and Marilu Henner's," he says, "and Maureen Stapleton's and Peter Boyle's. I'm just like an extended cameo -- I'm in it every time there needs to be some sleazy deed done."

A mostly wacko script gives him plenty of sleazy-deed opportunities. As Vermin, Piscopo (armed with a pencil mustache, a maniac's giggle and a .54 magnum that "shoots through schools") is out to get Keaton, all slicked down and dressed up in the title role of Johnny Dangerously, the mobster's mobster. (Also "a man's man, a ladies' man, tough, sensitive, soft, hard," to quote the publicity.)

"It was great working with Keaton," says Piscopo, who had done so once before when Keaton hosted an episode of "SNL." "I hope the movie turns out as funny as it was in the studio. I wish they could put out the outtakes -- we were breaking each other up all the time."

Piscopo credits director Amy Heckerling ("Fast Times at Ridgemont High") with keeping the "schtick factor" down (he thought it would be funny if Vermin snorted the gunpowder out of his gun barrel, and she said, "Well, Joe . . ."). And with forcing him not to play Vermin as an impersonation based on "real" gangster flicks.

"That's exactly the way I would've taken it," says Piscopo, who asked Heckerling for some tapes -- Heckerling being a Cagney buff ("She would've married Cagney," he says) who has, on videotape at home, old cops-and- robbers films up to here.

"You know, I wanted to see a Bogart, a Cagney, a Widmark film. Then it was getting close to shooting time and I wasn't getting the tapes. She says, 'No-no-no, you'll be fine.' So I developed the Vermin as an original character. Otherwise you would've seen me doing (he slides into a deep Bogart lisp) 'Hey, Jawnie -- come ovuh here.' Which is fine, except, gosh Joe, doesn't it sound a little like Bogie?"

So Piscopo says he used as models a couple of Italian relatives "who will remain unnamed."

In January, coincidentally enough, he'll be working on a film called "The Wise Guys," wherein he and Danny DeVito (the crooked D.A. in "Dangerously") portray two characters who get into trouble with the mob.

"Yeah," Piscopo says. "I only took the part because they're shooting it in Newark."