Green’s Dictionary of Slang

thatch-gallows n.

[all they are good for]

a worthless person.

[UK]Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Thatch Gallows a Rogue, Scoundrel or ill looking fellow.
[UK]Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.