Green’s Dictionary of Slang

(US) a victim.

1969

D. Pendleton Executioner (1973) 56: Emilio Giordano would not be any man’s funny bunny. [Ibid.] 57: If a damn dumb sergeant – a deserter at that – a common thief and gunman thought he could make Emilio Giordano roll over and play funny-bunny for him then [...] that damn dumb sergeant was going to die with a Giordano grapefuit up his ass.