Not THIS again! This is the same silliness that's been tried numerous times and you SHOULD know by now that NO ONE is calling Roman Catholics "arses". In fact, I doubt anyone even knew that little factoid (a questionable one) until you said it. The Moderator has also told you the same thing. Instead of trying to find offense in everything, why not accept that RC is just an acronym for Roman Catholic. Which, if I remember, you found fault with that one too.
The ignorance or insensitivity of the moderators and anti-Catholic Freepers aside, it is a painful issue to many Catholics. The term "Roman Catholic" was not used until the 17th century and can be found in no other language. The Church never refers to herself as "Roman Catholic". Whether you choose to use the term or not is between you and your Christian conscience.