Unfortunately, since the twitter box on profiles grabs its content directly from twitter, we can't impose the same filter on it that PC uses. So there isn't really anything we can do, though if it's really bothering you, you can click the arrows to the right of the box and hide the twitter box for everyone (I think) who has one.
Alternatively, if you notice someone swears a lot in their twitter feed, notify an admin and we'll talk to them about either toning it down or removing it from their profile since it really isn't allowed. But even I slip up now and then on twitter so I can't say I'm overly concerned about the occasional swear word slipping past our filters.