What is Natsa?
1.
stands for (you're) "not allowed to say anything"
The girlfriend picks a bad movie to go see, but you're NATSA (if you know what's good for you). Basically used in situations where you just have to bite your lip and keep your mouth shut: old people taking forever at the checkout, people in wheelchairs bumping into you, people inviting themselves into your activities, someone's kids spilling juice on your new carpet, etc.
See