Having attended a college with an enormous population of Japanese-nationals I can tell you, Japanese people are exceedingly polite. (A fact that might have escaped you if you share my anime addiction.) However, I was surprised when I began searching the net that many people claim that Japanese is a language with little or no profanity. Let me tell you, that is completely untrue.
The fact is that there are so many complex subtleties to the Japanese language that a simple lack of politeness is often the most effective insult. Many common verbs, like “to do” or “to give”, have multiple forms conveying various levels of respect, and your choice of verb can become extremely offensive. For example, the verb “yaru” (to give) is perfectly acceptable when giving food to a dog or when watering a plant, but is very condescending if used towards a person of equal or superior social stature. On the other hand, excessive politeness can be equally insulting. For example, “kisama” (my Lord), “otaku” (Your Respected House, which has come to mean “obsessive nerd” in modern Japanese), “onushi” (master) and “omae” (honorable one in front of me) are all pronouns which have come to be considered egregious insults in recent times. Consider this analogous to using “Your Highness” when addressing your mother.
One possible possible reason for the purported lack of curse words is superstition. In early Japan, Kotodama (literally, “word spirits”) were believed to appear when words were spoken, written, or even thought, and it was believed that they could become “tainted” or transformed into evil spirits by ill intentions.
Whatever the reason, it’s just not as satisfying to slight your Japanese-built car with a the wrong pronoun. Thus, I present my Gi-normous List of Japanese Cursing!
My favorite? When I was in college, I used to yell, “Inu Aka” (red dog) at anything that upset me. I’m not entirely sure why. I think I saw it in a movie. I stopped when I began drawing long stares at the local laundrymatte from people who looked as though they might be Japanese.
Many of these come directly from The Insult Monger’s Swearsaurus, but since the Swearsaurus isn’t alphabetized and is studded with pron, my list is a definite improvement.