Green’s Dictionary of Slang

diet of worms n.

In phrases

go to the diet of worms (v.) [pun on the proper name Diet of Worms, the meeting (1521) between Emperor Charles V and Martin Luther that effectively launched the Protestant Reformation + the action of worms on the dead body]

to die.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.