Short bloke has ecstasy habit (4)
I believe the answer is:
robe
'habit' is the definition.
(I've seen this before)
'short bloke has ecstasy' is the wordplay.
'short bloke' becomes 'rob' (short for Robert; 'short' indicates a short form).
'has' is a charade indicator (letters next to each other).
'ecstasy' becomes 'E' (informal term for the drug).
'rob'+'e'='ROBE'
(Other definitions for robe that I've seen before include "habit" , "Formal vestment" , "Formal attire" , "Loose outer garment" , "Gown, rich dress" .)