Do him a disservice - Idioms by The Free Dictionary
do (one) a disservice (redirected from do him a disservice)
do (one) a disservice
To do something that hinders or is detrimental to one. You'll really do your kids a disservice if you cater to their every whim.
do somebody a disˈservice do something that harms somebody and the opinion that other people have of them: The minister’s comments do teachers a great disservice.