As your child grows older, their social circle widens and so does yours, by proxy. You will meet other families at parks, in your neighborhood, preschool, and then the big one: school. By now you know that every child, even your own little angel, isn't always on their best behavior. So what do you do when you're faced with rude behavior from another person's child? It is bound to happen, so it's best to have a plan.
Your first encounter with misbehaving kids will definitely be your own. You can test different methods and consequences at home with your kid. Once you know what works, you might feel like you have a good system in place. What works for your own child isn't going to work for curbing sass in someone else's child, though.
It is tricky to find a way to set boundaries without overstepping with someone else's kid. You can't just lock yourself and your kid up and away from the world, so it is just a matter of time before you're faced with this problem. The most important thing you can do is adjust your attitude toward the child, and make conscientious decisions from there.