To behave foolishly and indulge in excess while one is young. The term has been around since at least the late sixteenth century. It alludes to sowing inferior wild grain instead of superior cultivated grain, analogous here to sexual promiscuity, and suggests that one will eventually outgrow such foolishness. As Thomas Hughes wrote in Tom Brown at Oxford (1861), “A young fellow must sow his wild oats,” but he then adds, “You can make nothing but a devil’s maxim of it.”