One can get so agitated about fine legal term (3,2,7)
I believe the answer is:
age of consent
'legal term' is the definition.
'one can get so agitated about fine' is the wordplay.
'agitated' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'fine' becomes 'f' (abbreviation).
'one'+'can'+'get'+'so'='onecangetso'
'onecangetso' with letters rearranged gives 'ageoconsent'.
'ageoconsent' going around 'f' is 'AGE OF CONSENT'.
(Other definitions for age of consent that I've seen before include "Legal majority?" , "Time when agreement becomes legally valid" , "Beyond which relations allowed" .)