Malicious bachelor causing irritation (6)
I believe the answer is:
bitchy
'malicious' is the definition.
('bitchy' can be similar in meaning to 'malicious')
'bachelor causing irritation' is the wordplay.
'bachelor' becomes 'b' (abbreviation e.g. BA=Bachelor of Arts).
'causing irritation' becomes 'itchy' (I've seen this before).
'b'+'itchy'='BITCHY'
(Other definitions for bitchy that I've seen before include "Unpleasant and spiteful like female dog" , "Catty" , "Speaking spitefully in manner of female canine" , "malicious" .)