Reprimand junky occasionally sitting in spilt beer (6)
I believe the answer is:
rebuke
'reprimand' is the definition.
('rebuke' can be a synonym of 'reprimand')
'junky occasionally sitting in spilt beer' is the wordplay.
'occasionally' means one should take alternating letters.
'sitting in' means one lot of letters goes inside another.
'spilt' indicates an anagram.
The alternate letters of 'junky' are 'uk'.
'beer' anagrammed gives 'rebe'.
'uk' going inside 'rebe' is 'REBUKE'.
(Other definitions for rebuke that I've seen before include "Scold (someone)" , "'Give out to, reproach (6)'" , "Sharply criticise" , "Tell off" , "Remonstration" .)