In a culture that prizes decorum, Hiroyuki Nishimura's Web video site and bulletin board are a chaotic — and sometimes obscene — free-for-all. Illustration: Christoph Niemann I'm sitting in a sterile white conference room waiting for Hiroyuki Nishimura. Japan is a nation where the 3:17 train arrives every day at 3:17 — not 3:16 or 3:18 — and Nishimura is 45 minutes late. The PR assistant who pains