I had various smutty words in my prediction file, which could be embarassing for me. I found the file using "strings" etc, if you just delete it it gets created afresh next time you type an unusual word which is good.

so yeah to get rid of all the pr0ntastic / personal words in your user dictionary file, use th Xterm and copy-paste this:

rm /home/user/.osso/dictionaries/.personal.dictionary

you may also want to check / remove the other file, to check:

strings /home/user/.osso/dictionaries/.used.dictionary | less

I didn't delete this file it only had a few recent non smutty words in it for me.

You may want to turn off word completion while typing uncacheworthy words, I suppose that would stop them getting stored.