Alcoholic drink not entirely bad, but not to be taken that seriously (8)
I believe the answer is:
flippant
'bad but not to be taken that seriously' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?
'alcoholic drink not entirely' is the wordplay.
'alcoholic drink' becomes 'flip' (I've seen this before).
'not entirely' becomes 'pant' (I am not sure about this - if you are sure you should believe this answer much more).
'flip'+'pant'='FLIPPANT'
Can you help me to learn more?
(Other definitions for flippant that I've seen before include "Impudent" , "Not serious or respectful" , "light" , "Cheeky" , "Not showing proper seriousness, disrespectful" .)