Stuffy fool has left in anger (7)
I believe the answer is:
airless
'stuffy' is the definition.
(synonyms)
'fool has left in anger' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'has' is an insertion indicator.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'anger' becomes 'ire' (ire is intense rage).
'l' inserted within 'ire' is 'irle'.
'ass' enclosing 'irle' is 'AIRLESS'.
(Other definitions for airless that I've seen before include "Lacking ventilation" , "Stifling" , "Still" , "Close" , "Unventilated" .)