One of the most annoying things that converts routinely see are these cradle-Catholics who, despite going to Catholic school for 12 years and early catechesis, know next to nothing about church teaching. They show up twice per year (Christmas and Easter) and call themselves Catholic despite the fact that nothing in their life reflects it. And then with a straight face, want to blame the church for their ignorance.
This usually comes up when they get caught flat-footed by some Jehovah's Witness or fundamentalist door-knocker who converses with them about their beliefs and why their unsuspecting mark should come and see for themselves how to "find Jesus." And it often works, too. Next thing you know, they've joined up and now feel the need to go "save" the poor, deluded Catholics from the faith of their fathers by arguing against beliefs they never understood in the first place.
Anyway, every time I see some yutz who clearly isn't living according to Catholic teaching referring to himself or herself as Catholic, I just want to grab them by the lapels and scream, "STOP CALLING YOURSELF THAT!!" I can't do that, of course, but if a person isn't going to at least try to live to a certain standard, I wish they would just drop the word Catholic out of their vocabulary altogether.