Star grabbing drink -- this is liable to go downhill! (3,3)
I believe the answer is:
ski run
'this is liable to go downhill' is the definition.
The definition suggests a singular noun which matches the answer.
'star grabbing drink' is the wordplay.
'star' becomes 'sun' (the Sun is a star).
'grabbing' is an insertion indicator.
'drink' becomes 'kir' (I've seen this before).
'sun' placed around 'kir' is 'SKI RUN'.
Can you help me to learn more?
(Other definitions for ski run that I've seen before include "Snow-covered slope" , "Winter sports slope" , "Downhill course in winter" , "Boggy, swampy" , "A trail for winter sportsmen" .)