Green’s Dictionary of Slang

(orig. milit.) a person, usu. in. comb. with a defining n., implying an occupation or job.

1942		F. Rhodes letter in Partridge DSUE (1961) II 991/1: Buster or basher is very common for mechanics, as in compass basher, instrument basher].
1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 112: Like all these artificial career-bashers he only heard you when you said something that could be taken as a dig.
1985		B. Humphries Traveller’s Tool 87: It’s mind-boggling to the average Samsonite-basher from England, the States or Down Under. [Ibid.] 114: I know that fantastic old Polish tarmac-basher is creaming his cassock for a nice long chin-wag with Yours Truly.