Thousand Island' first class cocktail (3,3)
I believe the answer is:
mai tai
'cocktail' is the definition.
(I've seen this before)
'thousand island' first class' is the wordplay.
'thousand' becomes 'm' (Roman numeral for a thousand).
'island'' becomes 'ait' (term for a small island).
'first class' becomes 'ai' (A1 - top quality).
'm'+'ait'+'ai'='MAI-TAI'
(Other definitions for mai tai that I've seen before include "Cocktail" , "drink?" .)