like water off a duck's back

like water off a duck's back (without effect) — как с гуся вода

Criticism falls away from him like water off a duck's back and he never worries about anything

(let sth) slide/roll off one's back

... Darwin typically let such criticisms slide off his back .
"Mea culpa," she said, and let it slide off her back , partially because it was the truth and because she meant to make amends now that she was home.(The Cougar Club)
..Help the children discern the difference between "big things" that actually needed to be worked through, and "little things" that one could choose to let just roll off one's back .

He will let any and all personal insults slide off his back.

From "Applying Living Wisdom's Practical Philosophies"

....This year I knew that I needed something outward and tangible to help my young students learn that they have a choice in the way that they respond to their feelings; that they are in charge, not their feelings. The well-known phrase, "Like water off a duck's back", came to mind. I made a little needle-felted duck, which I set on a dish at school. Next I collected many little discs of blue glass that were to represent drops of water. And finally I shared with my children the way that water actually does just roll right off of a duck's back, which led to the common phrase we use when someone chooses to let some troubling occurrence "roll off their back" instead of letting it upset them.
Next came the presentation of the little duck and the blue "drops". Each time a child chose to let something roll off his/her back instead of getting upset, he/she could announce it to the class and put a "drop" on the duck's back. Of course, the drop would immediately slide off the duck's back and land on the dish that the duck was sitting on. At the end of each day we would count the drops in the dish to see just how many times we had chosen to let some little thwarted desire or dissatisfaction roll off our backs instead of getting upset. As the number of drops grew, so did the children's joy and pride in their growing ability to choose how they would respond to the challenges they faced. One day when we had a particularly high number of drops in the dish at the end of the day (48), one child jubilantly called out, "Just imagine if we had had 48 upsets today instead of 48 times of letting it roll off our backs!" Smiles and expressions of awe spread across everyone's faces as they contemplated that possibility and realized what harmony and happiness had filled our day because of the choices they had made.
Certain areas of fine tuning happened over the days that followed, such as helping the children discern the difference between "big things" that actually needed to be worked through, and "little things" that one could choose to let just roll off one's back. That too was an important lesson; for there are many levels of problems and different situations call for different responses. They also learned to accept that we all have our natural ups and downs and some days it is easier to choose happiness than others.
In a remarkably short period of time the comment, "I'll just let it roll off my back", could be heard again and again in our classroom, on the playground and even at home. The number of upsets in our classroom diminished tremendously, and the children's friendships blossomed as harmony and caring took the place of over-indulgence in self-concern. (