As with anything, you have to sit down and look at what you're about to do.
Is it edgy? Okay, fine. Is this in good taste? Yes, go ahead. No? Rework it. Would this be offensive on a totally IC level, and not an OOC level? Yes? Good. And the most important question you need to ask yourself: Am I being an ass with this RP/letter/etc? If the answer is yes, scrap it until you can not be an ass about it.
Then you never have to worry.
