Och, Goyisha Kopf

A Jewish guy, Murry, has always been a good Jew. He came to synagogue every week, had friends there. One day he decides he wants to convert. His friends try, but cannot dissuade him. So finally he converts.
The next shabbos, there he is in shul again!
His friends go over to him, "Murry, what are you doing here? You converted!
You should be in Church! "
Says Murry striking his hand to his head, "Och, goyisha kopf!"