When a thing has gone Pear Shaped it's gone wrong, or at least not quite according to plan. The phrase originated in the first half of the twentieth century. The 1940 film My Little Chickadee, starring WC Fields and Mae West, includes the line, "I have some very definite pear-shaped ideas." It's actually thought that early RAF pilots are responsible for popularising the expression. While practising loops in the sky, a trainee pilot would often be unsuccessful in making a perfect circle and would flatten the plane's flight during the bottom section. Such mistakes were referred to as "going pear shaped."