You mentioned that your module will only return true/false and the calling program will decide what to do. However, it may help to look at the bigger picture - like what the calling program actually is going to do.

This one of the problems in dealing with natural language - so much depends on context. While certain words are only used in a vulgar context, there are also a lot of gray words besides "cock". You can even use normal words in a vulgar context, for example "up yours" can offend, so now you have to match phrases, not just words.

If the positives are sent to a moderator, you could be strict without too much problem. If they're deleted, you may want to be more lenient. Also, knowing what the calling program does, you may be able to provide better solutions, such as obfuscating gray area words ie: cocks = c****, or providing a true/false/maybe response.

I don't mean to throw you off track, but sometimes its too easy to get caught up in the details and miss other possible solutions to the overall problem.