What is the meaning of the old expression, "Thank your mother for the rabbits"?

The offhand nature of Wexford people gave rise to two peculiar sayings during the Second World War. Scarce commodities were passed around then and great thanks would be bestowed for the gift of an ounce or two of tea. The donor would shrug off the kind deed by saying, "Ah thank your mother for the rabbits, the soup was lovely!" It was a longwinded, "Ah, for nothing!"

In British and Irish English, the jocular phrase thank your mother for the rabbit(s) has been used:
– as an ironic expression of gratitude;
– as a goodbye.