Green’s Dictionary of Slang

coffin n.2

[var. on cuffin n. (1)]

a man, a fellow.

[UK]R. Holme Academy of Armory Ch. iii item 68c: Canting Terms used by Beggars, Vagabonds, Cheaters, Cripples and Bedlams. [...] Cove, or Cofe, Coffin or Cuffin, a Man, a Fellow.