Really fine at home -- always (4,1,5)
I believe the answer is:
well i never
'really' is the definition.
(both can be used to express surprise or disbelief)
'fine at home always' is the wordplay.
'fine' becomes 'well' (similar in meaning).
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'always' becomes 'ever' (synonyms).
'well'+'in'+'ever'='WELL I NEVER!'
(Other definitions for well i never that I've seen before include "Good gracious me!" , "that comes as a great shock" , "The call of the malingerer" , "Always sick, me?" , "That surprises me!" .)