Expression of annoyance about Wisconsin regional capital (6)
I believe the answer is:
darwin
'regional capital' is the definition.
(capital of the Northern Territory in Australia)
'expression of annoyance about wisconsin' is the wordplay.
'expression of annoyance' becomes 'darn' (mild swear word).
'about' is an insertion indicator.
'wisconsin' becomes 'WI' (abbreviation for Wisconsin).
'darn' going around 'wi' is 'DARWIN'.
(Other definitions for darwin that I've seen before include "Charles . . . . . ., author of 'The Origin of Species'" , "Author of On the Origin of Species, d.1882" , "Charles . . . . . ., great scientist of evolution" , "Charles ... who put forward theory of evolution" , "Naturalist with a theory on evolution" .)