Happy Endings/WMG

Penny is Jewish.
Penny has pretended to be Jewish on J-Date, taken up an Israeli martial art, and even created a Jewish alternate persona. Obviously her parents were Jewish, but converted when she was very young and kept this secret from her. She subconsciously remembers her Jewish childhood and this influences how she behaves.

Happy endings is Friends in an alternate universe
In this universe Monica and Ross aren't siblings, they are husband and wife, Joey had many women until he came out as a gay man with Rachel as the last girlfriend he had, Phoebe is Monica dumb blonde sister who dated Chandler for many years until the events of the first episode.