That we even have the term “practicing Catholic” is revealing. Despite living in New York for the last forty-four years, I don’t think I have ever heard any Jewish friend be called a “practicing Jew,” although more often Jews here are referred to by more specific adjectives: Orthodox, ultra-Orthodox, Conservative, liberal, Reform, secular. Most often, Jews who attend Sabbath services are “observant,” although I suspect that term may seem odd to the Haredi.
Anyhow, observant may be analogous to practicing.
But I also can’t recall ever hearing anybody describe themselves as a practicing Methodist or Presbyterian or Episcopalian or Lutheran, but, obviously, I haven’t been everywhere or spoken to everybody, so I haven’t heard everything. Still, I haven’t heard that.
To the extent that this is true, it’s because we Catholics know only too well that a whole lot of people who call themselves “Catholic” have very little knowledge of the faith and put very little of what they do know into use. They favor “a woman’s right to choose” and abortion, and they disfavor getting up on a Sunday morning and going to Mass. You could say they’re “out of practice,” the way I am with French and the drums, which were old passions allowed to cool.