Poor whisky is often served so (2,3,5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
on the rocks
I'm afraid I can't explain this answer.
Can you help me to learn more?
(Other definitions for on the rocks that I've seen before include "Drinks may be" , "Served neat with ice" , "In difficulties" , "Having problems" , "In trouble and failing" .)