On a downtown street, a Chinese assassin in a rubber Bill Clinton mask strolls along in slow motion. He fires a shotgun, killing four victims as the soundtrack twitters with ironic classical music. Recognize the movie reference? It's ''Point Break,'' it's ''Heat,'' it's ''A Clockwork Orange,'' it's a dozen of De Palma's lyrical gunfests. What it isn't is a sequence that serves any purpose -- that is, apart from fulfilling the desire of codirectors Johnnie To and Wai Ka-Fai to shoot it. In Fulltime Killer, To and Ka-Fai gather up their favorite American action clichés and try to inflate them into peak moments. Their bloodbath enthusiasm is, every so often, contagious, but the tale of Tok (Andy Lau), a sleek sociopath on the trail of O (Takashi Sorimachi), the most legendary of Asian hitmen, is too scattershot to take hold.