Theia comes with a built-in bad world filter. What this does is gives you the ability to enter words you don't want used, and what they should be replaced with.

To filter bad words, load up the "tools" page, and scroll down the "security settings" area, and look for a link reading "bad word filter / replacer" (admin tool 044).

There are only two fields in the form to add new entries; the first field is where you enter the word you want to filter out, and the second field is what you want instances of that word to be replaced with.

For example you could replace the "f-word" with f*ck or simply ****. You can use the bad filter to replace words however you desire, but take into consideration that you will probably need to filter different variants of the same word (ie: f*ck, f*cker, f*cking).

Things to consider...

Theia does not parse item or comment text on every page load, but instead the parsed text is cached. This means if you filter a new bad word, you will still see the word in items and posts that were created before then. To fix this, simply run the maintenance tools: "cache text for all posts" (admin tool 189) and "cache text for all items" (admin tool 190).