Words from fellow JINO (that's Jew In Name Only, or, as my sister called us, "Food Jews") Isaac Asimov, from his introduction to "Wandering Stars," a 1974 anthology of Jewish science fiction (which I strongly recommend you read).
Anyhow, Asimov spends the first portion of the introduction musing about why he was chosen to write the intro -- he had the Jewish last name and maternal line, the appreciation for Yiddish jokes and corned beef. But, he didn't practice at all -- no bar mitzvah, no shul. Still, he, like many of us, identified strongly as a cultural Jew, and took offense when people said otherwise:
Anyway, what with one thing and another, even without the bar mitzvah and the ritual, I feel I'm doing my bit and I grow impatient with those who take up a Jewisher-than-though attitude. Which reminds me of a phone conversation I once had with a gentleman whose real name I won't use (because I have forgotten it) but to whom I will give, at the proper time, a fictional name of equivalent aura.
It came about because the Boston Globe gave a bookfair at which I was asked to speak and at which I did speak. As it happened, the fair fell upon Rosh Hashannah, something I didn't realize, because unless someone tells me, I never know when it comes. This is not an excuse, just a statement, because if I had known it was Rosh Hashannah, I would have delivered my speech anyway.
The next day, however, I received a phone call from a stranger, who said he was Jewish, and who demanded to know why I had consented to talk on Rosh Hashannah. I explained, politely, that I didn't keep the holidays and that seemed to infuriate him. At once, he flung himself into a self-righteous lecture in which he descanted on my duties as a Jew, and ended by accusing me of trying to conceal my Jewishness.
Breathing a short prayer to the God of Aristotle, of Newton and of Einstein, I said quite calmly, "You have the advantage of me, sir, You know my name. I don't know yours. To whom am I speaking?" And the Lord God of Science proved to be on the job, for the man on the phone answered, "My name is Jackson Davenport."
I said, "Really? Well, my name, as you know, is Isaac Asimov, and if I were trying to conceal my Jewishness, the very first move I would make would be to change my name to Jackson Davenport."
Somehow that ended the conversation.
Best wishes for an easy convincing-your-grandmother-you fasted-without-actually-lying when you go to her house to break it tonight.
:D