Regularly ignored disdain of jerk being foolish (7)
I believe the answer is:
idiotic
'foolish' is the definition.
(thesaurus)
'regularly ignored disdain of jerk' is the wordplay.
'regularly ignored' indicates alternate letters.
'jerk' becomes 'tic' (I've seen this before).
'disdain'+'of'='disdainof'
The alternate letters of 'disdainof' are 'idio'.
'idio'+'tic'='IDIOTIC'
'being' is the link.
(Other definitions for idiotic that I've seen before include "Daft" , "description of Dostoevsky hero?" , "Senseless" , "Half witted" , "Ridiculous" .)