Average chap consumes Ecstasy (4)
I believe the answer is:
mean
'average' is the definition.
(type of average)
'chap consumes ecstasy' is the wordplay.
'chap' becomes 'man' (I've seen this before**).
'consumes' indicates putting letters inside.
'ecstasy' becomes 'e' (informal term for the drug).
'man' going around 'e' is 'MEAN'.
(Other definitions for mean that I've seen before include "of little value" , "Far from noble" , "mercenary" , "Import" , "Nasty" .)