Regularly ignored staid, hirsute brute (6)
I believe the answer is:
sadist
'brute' is the definition.
(a sadist enjoys inflicting pain)
'regularly ignored staid hirsute' is the wordplay.
'regularly ignored' means one should take alternating letters (letters removed at regular intervals).
'staid'+'hirsute'='staidhirsute'
The alternating letters of 'staidhirsute' are 'SADIST'.
(Other definitions for sadist that I've seen before include "Rub out, obliterate" , "One who enjoys cruelty" , "One deriving pleasure from inflicting pain on others" , "One who takes delight in cruelty" , "Person who enjoys inflicting pain on others" .)