( informal ) used to say that sth, especially criticism, has no effect on sb/sth :
I can't tell my son what to do; it's water off a duck's back with him.
( informal ) used to say that sth, especially criticism, has no effect on sb/sth :
I can't tell my son what to do; it's water off a duck's back with him.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005