Green’s Dictionary of Slang

bum-fluff n.

also bum-bluff
[bum n.1 (1) + SE fluff]

1. [late 19C+] the very light growth of hair on the face of a boy who is on the verge of needing to shave.

2. attrib. use of sense 1.

3. [1940s+] (Aus.) empty talk, nonsense.

4. [1990s+] pubic hair.

5. [2000s] a term of address, whether abuse or affection.

In derivatives

bumfluffy (adj.)

[2000s] sparse, thin.