Hi,

i think diffrent childern react diffrently to certain things,With DD the opposite actually worked,She heard some people saying ''shut up'' and then decided to repeat it,so first i told her that it was not a nice thing to say and not to say it.The second time she said it i looked at her dad and shook my head and said ''look daddy she said a bad word that only naughty people say'',she just stared at me and got sad.Well she hasnt said it since and a couple of times while im joking around with DH and i say oh shut up,she looks at me sternly and says MUM thats a bad word so i say oh no your right im sorry.
But like i said each kid has their own thing that works on them.So you gotta see what makes him feel bad that he said something bad.And if he does it for attention then the ignoring techniqe might be best..
good luck