Green’s Dictionary of Slang

(US black) copulation.

1926		Van Vechten Nigger Heaven 208: Out fo’ a little hootchie-pap, Ah pre-sume, another voice commented.
1936		G. Kersh Men Are So Ardent 180: Another voice emerged: ‘. . . have just heard Ray Pipe and his band broadcasting from the Belgravia Hotel. Miss Totty Jerusalem will now sing “Hootchie-pap”’.