lay-down misère , n. — Green’s Dictionary of Slang

lay-down misère n.

[card-playing imagery; in the game of misère, ‘lay down misere, or misere ouvert is a 500 bid where the player is so sure of losing every trick that they undertake to do so with their cards placed face-up on the table’ (Wikipedia)]]

(Aus.) an absolute certainty.

1996

J. Byrell Lairs, Urgers & Coat-Tuggers 67: ‘Rising fast [i.e. a race horse] is a fair dinkum lay-down misère. And that’s the stable oil’.