Ratty's boat kept in hideaway capsized (6)
I believe the answer is:
narked
'ratty's' is the definition.
(both can mean annoyed)
'boat kept in hideaway capsized' is the wordplay.
'boat' becomes 'ark' (ark is a kind of boat).
'kept in' means one lot of letters goes inside another.
'hideaway' becomes 'den' (synonyms).
'capsized' is a reversal indicator.
'den' reversed gives 'ned'.
'ark' inserted within 'ned' is 'NARKED'.
(Other definitions for narked that I've seen before include "Nettled" , "Cross" , "Annoyed (informal)" , "'Vexed, riled (6)'" , "Annoyed - upset - irritated" .)