Whats in A name?

An 'A' can make the world of difference sometimes.

He is black - Ok. He is a black - ol' skool racism.
She is gay - Fine. She is A gay - Not cool but ironically funny.
I love four year olds - fine. I love A four year old - Not fine.

The case where I am not sure this does work is religion.
He is Jewish. Or, He is A Jew.
She is Christian versus she is A Christian.