Green’s Dictionary of Slang

a general insult, i.e. one who is destined for the gallows.

1570		P. Levins Manipulus Vocabulorum 81/4: A Gallowclapper, furcifer.
1583		A. Golding Calvin on Deut. 305: It is not only the gallowes-clappers that say so I meane those whose faultes and crymes are manifest.
1638		R. Brome Antipodes II ix: Come, come, ye Gallows-clappers.