The phrase “Barmecide feast” (or banquet) comes from the “Story of the Barber’s Sixth Brother” in Arabian Nights.
A poor beggar, Schacabac, without food for several days, asked for bread at the door of the rich Persian noble, Barmecide.
To his amazement he was invited to the table.
Servants brought golden platter after golden platter, and his host urged him to help himself freely, but there was not a thing upon any of the platters.
Nevertheless the beggar entered into the spirit of the jest, pretended to pile his plate full and to eat bountifully, and when, at the end of the repast, an empty jug of wine was brought, Schacabac pretended to fill and refill his goblet frequently and, eventually, to become quite drunk.
In this feigned state he boxed his host heartily on the ears.
This and the good nature of the beggar so delighted Barmecide that he then had a real banquet brought to the table.
Thus, nowadays, a Barmecide is one who offers an unreal or disappointing benefit, and a Barmecide feast or banquet is a meal that, however inviting to the eye, fails to live up to expectations.