Becomes touchy when one pours the cat a drink (4,2)
I believe the answer is:
acts up
'becomes touchy when one pours the' is the definition.
I can't judge whether this defines the answer.
'cat a drink' is the wordplay.
I cannot really see how this works, but
an anagram of 'cat' is 'act' which is located in the answer.
'drink' could be 'sup' (to sup is to drink) and 'sup' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for acts up that I've seen before include "Malfunctions" , "Behaves in a troublesome way" , "Fails to function properly or behaves badly" , "Causes trouble or misbehaves" , "Carries on" .)