When you study a foreign language, the first thing you usually learn are the "naughty" words -- that's just human nature. However, students of Japanese are often surprised to learn that most of the bad words they're used to in English don't map over very well. The most common Japanese insults include baka (BAH-kah, stupid), aho (ah-HO, the Osaka-ben version of the same word), and boke (BOH-kay, basically meaning "nim-wit"). Almost all the anatomical words you may be used to just don't work in Japanese, nor does the "F" word, which doesn't even exist, except occasionally in English as a foreign loan word. The most basic Japanese swear word is probably kuso (KOO-soh), the "S" word, yet it's interesting to note that it's not considered a bad word, as it's used in children's anime like Yu-Gi-Oh quite often and no one thinks anything of it. It addition to the primary meaning, the word kuso can also refer to various bodily products. The stuff that comes out of your nose is hana-kuso (nose-sh--), and ear wax is mimi-kuso (ear-sh--). The stuff that builds up in your eyes as you sleep is me-kuso (MEH-kuso), and plaque on your teeth is called ha-kuso. Now you know some interesting (and probably useless) Japanese vocabulary words!
The word kuso ("shit!") is a common occurrence in anime and manga. and no one cares.