To stand BUFF,
is a Phrase used of an obstinate hardened Rogue, who in a Robbery will not be daunted at Resistance or Opposition, or leave his Com-rogues in the Lurch, or a hardened Rogue who will confess nothing.
The Vulgar Tongue originally collected by Grose, 1811.
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).