Literal translation
he cares about something as much as the ace of spades
Meaning
he couldn't care less about it
Explanation
The phrase signals total contempt or indifference toward something. The verb garça originally meant to fling, to throw with force, hence the idea of casting the thing far away, rejecting it without ceremony, before sliding into the figurative sense of not caring at all about it. The comparison rests on the ace of spades, a card whose value, depending on the game and the region, can be seen as the weakest or most insignificant in the whole deck: to care about something as much as the ace of spades is to give it no weight, no bearing on any decision. The turn of phrase belongs to card-game vocabulary, very present in Provençal popular comparisons, where belote and tarot terms supply a stock of images for value, luck and chance. The register is familiar, cheerfully offhand, used to signal that one will not let a threat, an opinion, or a criticism get under one's skin.