Go pear-shaped

Uncertain; the following etymologies have been suggested: * From the image of a solid rectangle “slipping down” into a pear shape, thus “the bottom drops out”. ** Similar thoughts about the work of either glassblowers or potters involve a theme of the work trending toward a sagging shape; such speculations may be only folk etymology. * From the image of a balloon or football losing its spherical shape after being punctured. * From an idea that people who shoulder the work — who have the responsibility on their shoulders — may descend into shirking, in which case their broad shoulders diminish as their body becomes pear-shaped. Apparently the term was originally Royal Air Force slang, but came into common use by the 1990s.