Stickler for the law gets all flustered about one (8)
I believe the answer is:
legalist
'stickler for the law' is the definition.
(someone strictly adhering to the law)
'gets all flustered about one' is the wordplay.
'flustered' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'gets'+'all'='getsall'
'getsall' is an anagram of 'legalst'.
'legalst' enclosing 'i' is 'LEGALIST'.
(Other definitions for legalist that I've seen before include "Strict lawyer" , "One adhering to the detail of the law" .)