wiki-
Obsolete meanings of the term "haberdasher" refer to a "dealer in, or maker of, hats and caps".
it used to be a term for hat maker, thus the joke at the end of spinal tap...
"if you could have any other job in the world what job would you like to do"
"any job?, well that's easy I'd like to be a haberdasher, or maybe a chapeau shop owner"
the reason it is funny is he lists 2 jobs but really they are the same job.