To be cagged. To be sulky or out of humour. The cove carries the cag; the man is vexed or sullen.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Cagg * Cag MaggNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes