Out-of-date dope snorted by half-cut Pete (5)
I believe the answer is:
passe
'out-of-date' is the definition.
(synonyms)
'dope snorted by half-cut pete' is the wordplay.
I cannot really understand how this works, but
'dope' could be 'ass' (both can mean a stupid person) and 'ass' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for passe that I've seen before include "Out-of-date (French)" , "No longer in fashion" , "dated" , "Old fashioned - in France" , "Master key - picture mounting" .)