Let's flip a coin for heads or tails to decide.
heads or tails
idiomThe practice of flipping a coin in the air, to choose between two alternatives based on which side lands face up.
Origin
first recorded 19th c.Attested since at least 1833, on the second page of Galignani's Messenger: "amusing themselves by pitching quoits, spoiling halfpence at heads or tails with the gingerbread merchants, drinking beer, smoking, etc".
We could not agree on which movie to watch, so we settled it with a quick game of heads or tails.
Faced with two equally unappealing options, he decided to leave his fate to chance by calling heads or tails on a spinning coin.