It has been said that there are few cusswords in Japanese. There are some words like baka and aho, I must admit I only really heard baka said once to realize how much meaning can be contained in one word. I think the word baka is the most foulest word in the Japanese language.
It is also possible to sound foul mouthed simply by staying in the lowest level of politeness.
Their are basically 4 levels of politeness in Japanese. From least polite to talking with the emporer polite, there are 4 grades or levels that are distinctive in their use.
Lets take verbs for example. The verb
iku becomes ukagau,
iu becomes ossharu,
suru becomes nasaru.
I have heard aho - similiar to the English words a**hole or dickweed perhaps.
1st level - Honorific speech. The level of highest politeness. In this level you are in essence raising the status of the person with whom you are talking to. Your speech determines their high status and this elates them. The feeling you get when being spoken to in honorific Japanese is that you are a member of a royal family.
When I was being spoken to in this honorific speech called keigo, I felt powerful. It made me feel very wanted or in some sense loved. It also made me feel like I was needed. I felt like I belonged and that they wanted me there. I certainly had a place. The words spoken make you feel comfortable and you also have a feeling of responsibility that comes with this nobility. Thinking in terms of maslowes heirarchy of needs being spoken to in keigo would fit the bill and fulfill that level in the pyramid of Maslowes heirarchy of needs.
Now with the next level politeness you have verbs ending with masu and the use of desu makes them straight polite level verbs.