A street in New York is unpleasant (5)
I believe the answer is:
nasty
'unpleasant' is the definition.
(nasty can mean unpleasant or horrible)
'a street in new york' is the wordplay.
'street' becomes 'st' (abbreviation).
'in' is an insertion indicator.
'new york' becomes 'ny'.
'a'+'st'='ast'
'ast' inserted within 'ny' is 'NASTY'.
'is' acts as a link.
(Other definitions for nasty that I've seen before include "rank" , "Foul" , "Vile" , "Disagreeable" , "Disgusting" .)