I don’t doubt the abbreviation of RC came first and someone just saw the opportunity to corrupt it.
Considering the pronunciation isn’t even that close, since saying something that sounds like are-see is not the same as saying something that sounds like ars, it’s really just a matter of how offended someone chooses to be.
Nobody is pronouncing the letters *R* and *C* as *ars*, they are being pronounced as an *R* and a *C*.
The pronunciation may not be that close in Tulsa or East Cowpie or where ever you are, but it is indistinguishable from arse from Dingle to Derry.