Of course it's not a "proper" term, but it's so long been an "in" usage, people who make a fuss about it are clearly not Anglicans. (I can't speak for RCs.)
It's sort of like the U.S. term "Whisk(e)ypalians" -- an internal jest that might look offensive, pejorative and derogatory to an outsider.
(But use it in those contexts and you may have a battle on your hands.)
Q: "Do Episcopalians believe in smoking and drinking?"
A: "Yes, but they're not necessary for salvation."
"Episcopagan" may be more accurate these days . . .