R.R.
I "pretend" not to see it and announce to the air around me "I KNOW that there is not a child behind me making disrespectful faces at me. Because I KNOW that the child KNOWS how much trouble they will get in if I see it".
If my child were to do it directly to my face, I would grab them by the shoulders, get down on their level and say sternly "That is VERY disrespectful, and I do not tolerate disrespect. You have 3 seconds to apologize to me"
To me this falls under the category of basic respect, and does need addressed!