When I heard that playwright Joshua Harmon’s Bad Jews was the talk of London’s theatreland I thought I’d better check it out. For the first 15 minutes I wasn’t quite sure what all the fuss was about as I watched a couple of privileged twentysomething cousins – Daphna (Jenna Augen) and Jonah (Joe Cohen) – waking up and shooting the breeze in Jonah’s small but enviable Manhattan apartment.