Somebody who was widdiful deserved to be hanged.
The story behind it starts with the northern English and Scottish wordwiddy or widdie, local forms of the standard English withy, a flexible branch from a tree such as willow used to make baskets or to tie or fasten things together. One sense was of a band or rope made of intertwined withies.
Later it came to mean a halter and in particular a hangman’s rope. Tocheat the widdy meant to escape hanging. By an obvious transfer the sense of gallows-bird grew up, one destined to fill a widdy. This is a modern example:
”Will you shut the bloody noise off, you bloody widdiful!” Philips said in a shout that was nearly a scream.
The Reaches, by David Drake, 2003.
The word weakened in its later history in Scotland, turning into a joking term for somebody who was merely a scamp or scoundrel. It has been recorded in Yorkshire dialect in a very different sense, one derived from the idea of a withy being tough and durable:
WIDDIFUL, Industrious, laborious, plodding. It is applicable to a hard-working man, who never complains of fatigue, and is derived from widdy; of such a character it is often said, “he’s as tough as a widdy.”
The Dialect of Craven, in the West-Riding of the County of York, by William Carr, 1828.