Who Is a Jew?

I find it hilarious (and somewhat distasteful) that most Orthodox Jews are perfectly comfortable sitting around a Shabbat table and chatting about who is Jewish and who is not. It doesn't matter if their subject's family converted to Christianity four generations ago, only to become lapsed. It's still, "Did you know that Priscilla is Jewsh? She doesn't know, but her great-great-great-great grandmother lit shabbos candles! Her kids will be Jewish!" Forget about the practicing reform Jew down the block whose father is Jewish but mother isn't. He's just faking.