Green’s Dictionary of Slang

(Irish/Scots/Ulster) a gossip, a tattle-tale; also attrib.

1824		J. Mactaggart Scottish Gallovidian Encyc. 136: Clashbag — A person fuill of low mean stories.
1878		Falkirk Herald 21 Nov. 2/1: We would make short work of thi silly trumpeting and clash-bag diversion.
1910		P.W. Joyce Eng. As We Speak It In Ireland.
1913		Southern Reporter 21 Aug. 3/9: We fervently hope [...] that nae local clash-bag ’ill be as bluid-thirsty as tae convey even a whisper.
1997		Share Slanguage.