the apple of discord

There was a wedding on Mount Olympus, and every god and goddess had been invited — every one, that is, but Eris, the spirit of strife. She was left off the guest list on purpose, for who wants quarrelling at a wedding? But a slighted goddess does not simply stay home.

She came to the feast unseen, and she brought a single golden apple. Onto it she had scratched two small words — For the fairest — and she rolled it quietly into the middle of the hall, then slipped away to watch.

At once three goddesses reached for it. Hera, queen of the gods; Athena, wise in war; and Aphrodite, goddess of love — each was certain the prize was meant for her, and none would yield. What began as a glance became a boast, and the boast became a bitter, blazing argument that even Zeus dared not settle.

The choice was passed to a mortal shepherd named Paris, and his fateful judgment set the whole world alight — for the apple's quarrel led straight to the ten-year war that burned the towers of Troy. One small golden fruit, and a wedding's joy curdled into a decade of ruin.

So we call anything an apple of discord when it is a small, tempting thing that drops into the middle of a group and sets everyone at one another's throats.