Green’s Dictionary of Slang

bub n.3

[SE bubby, a little boy]

1. [early 19C+] (US) a boy, esp. when used as derog. form of address, implying youth, insignificance etc.

2. (Aus. / N.Z. ) a baby.

3. [1980s+] (US campus) a person devoid of redeeming qualities.