Water off a duck’s back is an idiomatic expression that is used to neglect or ignore unwanted criticism.
The phrase is generally applied when somebody is unaffected by an insult, and they don’t appear to notice or care about it.
Ducks are a kind of bird species that spend their majority of their lives around bodies of water.
Throughout evolution, their feathers have developed an oily surface that makes the birds’ body water-repellent.
This effect can be often observed in nature. When ducks get wet, water simply rolls off their backs with ease. Hence came the expression: water off a duck’s back.
Early usage of the expression dates back to 19th-century America, when it was used initially in a more literal sense.
Back then, it was used in print to advertise hunting gear and water-resistant equipment.
Eventually, the term became part of everyday language use, sometimes appearing in pop-culture as well.
The TV show RuPaul’s Drag Race featured the idiom in Season 5 as a catchphrase for one of the show’s contenders.