Most upset about that woman's flask (7)
I believe the answer is:
thermos
'flask' is the definition.
(I know that thermos is a type of vacuum bottle)
'most upset about that woman's' is the wordplay.
'upset' is an anagram indicator.
'about' means one lot of letters goes inside another.
'that woman's' becomes 'her' (belonging to a woman).
'most' is an anagram of 'tmos'.
'tmos' placed around 'her' is 'THERMOS'.
(Other definitions for thermos that I've seen before include "Flask trade mark" , "Heat-retaining flask for mothers" , "Container to retain heat" , "Vacuum flask for mothers" .)