Iwas told this in a pub (by a jewish ex-colleague) many years ago, so any errors are mine.
David, the son of Orthodox parents is married "out of the faith", his parents have eventually come to accept the fact and his mother comes to their home for a visit. While David's wife is collecting the children from nursery, his mother turns to David, "David, I'm saddened, I look in the 'fridge, you have milk and meat together, you've only one set of pans, I know for a fact that you sometimes work on the Sabbeth, you never cover your head<1>. Tell me son, Are you still circumcised?"
<1> I can't remember the name of the skullcap - W