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 universeIn 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.
Happy Endings takes place in the same universe as It's Always Sunny In PhiladelphiaRegan Burns appears as the manager of a pool club in the episode "Mac and Charlie: White Trash" during season season 6 of Always Sunny. He then appears in season 3 of Happy Endings as the manager of a private tennis club Brad and Jane are trying to join. Either the company who owns the tennis club in Chicago also owns the private pool in Philadelphia and he got transferred or he simply jumped on a great job opportunity in a not so far away city some time between 2010 and 2013.