Green’s Dictionary of Slang

rag box n.

also rag shop
[rag n.1 (3a) + SE box/shop ]

1. the mouth.

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[UK]Kipling ‘The Big Drunk Draf’’ in Soldiers Three (1907) 35: By this you will larn to kape a civil tongue in your rag-box.

2. (US black) in ext. use of sense 1, the vagina [? also box n.1 (1a)].

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[US]R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].

In exclamations

shut your rag-box!

shut up! be quiet!

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Kipling in Scots Observer 28 June 149/1: Now all you recruities what’s drafted to-day, You shut up your rag-box an’ ’ark to my lay.