apple of discord
Something that causes unhappiness or trouble. That stupid prom dress has been their apple of discord—they've been fighting over who gets to wear it for days now! Why aren't you talking to Mary Beth? What is the apple of discord here?
apple of discord
a subject of dissension. This expression refers to the Greek myth in which a golden apple inscribed ‘for the fairest’ was contended for by the goddesses Hera, Athene, and Aphrodite.