If anyone out there really don't know what
"hentai" is, here's the clou:
1.japanese for anime/manga with more or less
  explicit sexual content( in japan mainly used
  for the less drastic stuff (the real hard
  pornographic stuff is called "etchi"(jap."h")
  and marked with big "H"on the cover)
2.japanese slang to call somebody a "pervert"
  in a funny way

Well,as I always say: I'm into manga/anime
for a longer time but I'm only human
so please correct me if I made a mistake.