Italy's favorite comedian has scored big at home with "Il Mostro," the Boot's highest-grossing ($35 million) film ever. But American filmgoers, familiar with the talented Benigni from "Johnny Stec-chino" or "Down by Law," may be forgiven for wondering what all the fuss is about. This film is a tepid, unfunny variation on the mistaken-identity premise; here, Benigni is cast as Loris, a down-and-out con artist who's presumed to be a vicious rapist and serial killer. As the hapless suspect, Benigni mugs and gesticu-lates wildly, but his routines like one where a lit cigarette falls down his pants are awfully old hat. Some jokes about molestation and murder are in bad taste. "The Monster" has its virtues, notably a charming Nicoletta Braschi as an undercover policewoman out to trap Loris. But there's only so much she (and Benigni) can do with such lame material. Starring Roberto Benigni, Nicoletta Braschi and Michel Blanc. Directed by Roberto Benigni. Written by Roberto Benigni and Vincenzo Cer-ami. Produced by Roberto Benigni and Yves Attal. A CFP release. Comedy. Italian-language; subtitled. Unrated. Running time: 110 min.