do somebody a/no service

do (one) a service

To help or aid one. Sharon did me a service by getting that jammed paper out of the printer.
See also: service

do (one) no service

To do something that hinders or is detrimental for one. You do your kids no service by catering to their every whim.
See also: no, service

do somebody a/no ˈservice

(formal) do something that is helpful/not helpful to somebody: She was doing herself no service by remaining silent.
See also: no, service, somebody