Green’s Dictionary of Slang

blaitie bum n.

also bummillbaty

(Scot.) a fool .

[Scot]D. Lyndsay Satyre of Thrie Estaits I (1604) 9: Gif if be sin to tak ane Kaity, Or to leif like ane bummillbaty. [Ibid.] 95: Quhair Devil gat we this ill-fairde blatie bum?