Vicious American disembowelled sweetheart in New York (5)
I believe the answer is:
nasty
'vicious' is the definition.
(thesaurus)
'american disembowelled sweetheart in new york' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'disembowelled' says to hollow out the word (remove centre letters).
'in' indicates putting letters inside.
'new york' becomes 'ny'.
'sweetheart' with its middle removed is 'st'.
'a'+'st'='ast'
'ast' going into 'ny' is 'NASTY'.
(Other definitions for nasty that I've seen before include "Spiteful and unkind" , "Beastly" , "Horrible" , "Not nice" , "Highly unpleasant" .)