If you wrote it yourself, definitely say so, as I will give it preferential treatment. Search the RHF Joke Archives before submitting to make sure your joke hasn't already been done. This is not easy to do, since many jokes come in different forms with different people and places substituted. However, if you submit a joke that is a virtual duplicate of one in the archives, we will be royally ticked at you. Don't send entire copyrighted works.
Excerpts are OK, if they take the form of news, or a review of the work.
Don't send me professional columns like Dave Barry's. I just can't send these out without permission. If your submission is original, tell me that clearly. If it's topical and original, mail to topical, and say at the top that you wrote it. If you see a copyrighted work you would like to submit, call and ask the copyright holder.