Showing very unfriendly manner on small island (6)
I believe the answer is:
sicily
'island' is the definition.
(Sicily is an example)
'showing very unfriendly manner on small' is the wordplay.
'showing very unfriendly manner' becomes 'icily' (in an icy or unfriendly way).
'on' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'icily' after 's' is 'SICILY'.
(Other definitions for sicily that I've seen before include "Largest Mediterranean island" , "Etna's island" , "Italian island, capital Palermo" , "Large Mediterranean island off Italy" , "Italian island home of the mafia" .)