If you say to someone, "**** you", the censor isn't actually protecting the recipient from the content of the message. Maybe this is just a flaw with censors as a whole (like beeps) but it's like you're not even trying to hide what was said. With just a little context you can figure out what pretty much anything was meant to say. Therefore, remove the content of the message entirely or simply prevent an offensive post from being sent.
The main reason I've always wanted the former was because of how hilarious it sounds to me.
I just love the idea of pissing someone off and them retorting, "[BLANK] YOU!"
The latter could create a situation like with Cofagrigus in Black/White, and frankly wouldn't be nearly as fun. If you cut the whole word out, it might be more difficult to tell when someone is being offensive, but let's look at it this way:
Suppose you're upset, and you try to scream profanities at someone. Well, it all got cut out of the post so you start laughing at how ridiculous it looks instead. Now you're in a good mood and you get over it and everyone is happy. Move on.
I know this is a more minor suggestion, but it's been bugging me a little bit.