This reflects either collosal ignorance or arrogance. I haven't decided which. Personally, I have never heard anyone express the idea that a Catholic is not a Christian.
BTW, do you believe that Roman Catholics are Christians? Do you view Roman Cathoics as pagans?
I believe that anyone professing belief in Christ Jesus as Savior and Son of God is a Christian. Now, let me ask you: Do you believe that anyone not a Roman Catholic can be a Christian?
"Personally, I have never heard anyone express the idea that a Catholic is not a Christian."
Take a look:
http://www.born-again-christian.info/catholics.htm
http://www.jesus-is-lord.com/cath.htm
http://www.carm.org/catholic/saved.htm
http://www.chick.com/information/religions/catholicism/
Do a Google search for "Catholics are not Christians" (and similar search parameters), and you might discover that the belief is more widespread than you thought.
"Do you believe that anyone not a Roman Catholic can be a Christian?"
Of course.