There is a famous joke that I may have told several times already. A son comes home and tells his Jewish atheist father about X-mas, the tree, the mamzer, the whole spil, and asks to have an X-mas tree. The father starts screaming at him that they are Jewish and they don’t do this. The son asks: “But I thought we don’t believe in G-d?..” The father answers: “Yes, but it’s the Jewish G-d we don’t believe in.”
I heard this story first time from my rabbi when I told him about a Jewish — but not religious — scientist from Russia who came to the US on a job offer. Her boss was showing her around and brought her to a reform shull. She entered, saw the rabbi without kippa, men and women sitting together, turned around and walked out. She may not keep Shabbos or kosher, but she knows treif when she sees it.
This story reminded me of the joke and the scientist. Especially the last sentence.