The best way for you to ensure that people know you can't text back! No matter whether you are driving, are in a meeting, at the movies, and are participating in other private activities, let them know that you are busy!
When you install Don't Text and Drive, you are opening a whole new world of not dealing with text messages. Let people know you are busy. Let them know you have a life and you value it. Or more importantly, that you're at the theater and you don't want popcorn thrown at you!
Keep people off your back!