Green’s Dictionary of Slang

duff n.2

[west Yorks. dial. duff, the posterior]

1. [mid-19C+] the buttocks.

2. [late 19C] the vagina.

In compounds

duff-flogger (n.)

[1930s] (US) a male masturbator.

In phrases

duff around (v.)

[20C+] to sit about, to act lazily.

fluff the duff (v.)

1. [1950s] to shirk, to act lazily.

2. [1980s+] (US gay) to have anal intercourse.

shoot one’s duff (v.)

[1980s+] to ejaculate.