Well said, dragonchild.

Before I go into makeing the matter even much worse I will start making it just a little more perilous. You said:

For example, you know these words:

• fcuking
• pneis
• ashosle

m/f[1ciknu]{5}g/
m/p[1ein]{3}s/     #2
m/a[0hlos]{5}e/
[download]

these work very well in some cases, but will do more than they are supposed to do in others.
Take the obvious #2: so what's wrong with pines?
But you probably won't know the less obvious all the time.

Much more frightening than this is, once you started, your clients will likely want you to add bad words from Spanish, German, Yiddish, Portuguese, Russian, French, Finnish, Swedish, Polish and so on.
Once you do that, there are no good words remaining. Almost all everyday language words do mean something very rude an a number of languages...
there's no achieving the goal your task I'm afraid.

Cheerio, Sören