(not offensive to anyone whose actual profession is or was a chimney-sweep):
a) a very offensive term used by white people to insult other white people who are not only pro-miscegenation but are, regardless of actual truth, perceived to have a non-white
significant other.
b) a so-so offensive term for a grease-monkey or a janitor
c) a very offensive term used by white middle class intellectuals to insult members of the white urban
working class who hang out exclusively with black members of the urban
working class and who become more 'black' than 'white' in terms of 'manners', music taste, etc.
if you are called a chimney-sweep, especially
definitions a) and c) above
you are not only pro-miscegenation, and don't really care about
interracial marriages and stuff, but you have no clue what the term ehre weiBen kultur means.