Rabid eccentric in short time getting a piece of one's mind! (8)

'a piece of one's mind' is the definition.
(I know that midbrain is part of brain)

'rabid eccentric in short time' is the wordplay.
'eccentric' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'short time' becomes 'min' (short for minute; 'short' asks for a short form).
'rabid' is an anagram of 'idbra'.
'idbra' put inside 'min' is 'MIDBRAIN'.

'getting' is the link.