Second-rate beer? Drunk endlessly threatening (7)
I believe the answer is:
baleful
'threatening' is the definition.
(I know that threatening can be written as baleful)
'second-rate beer? drunk endlessly' is the wordplay.
'second rate' becomes 'b'.
'beer?' becomes 'ale' (type of beer).
'drunk endlessly' becomes 'ful' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'b'+'ale'+'ful'='BALEFUL'
Can you help me to learn more?
(Other definitions for baleful that I've seen before include "Malevolent" , "Menacing - vindictive" , "Menacing - dejected" , "Threatening or foreshadowing evil" , "Menacing - gloomy" .)