Whisky served in this way may be ruined? (2,3,5)
I believe the answer is:
on the rocks
'be ruined?' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for on the rocks that I've seen before include "Having problems" , "In difficulties" , "Ruined" , "Served neat with ice" , "In trouble and failing" .)