Huh, I voted "yep!" but after reading this thread, I see that I misunderstood the expression : "to break a NAP".
In my mind, if I have a NAP 5 with a player and if I say : "end of the NAP, I'll attack you in 5 turns", that I called breaking the NAP. Just a normal thing. I voted "yes" with that meaning in mind.
Now, I see that "breaking a NAP" would mean here me telling the guy : "Hello ! We have a NAP 5 but I'll attack you in 2 turns anyway because [whatever]".
Here, my answer is definitely : no, I don't break any NAP because it's useless to make promises if you don't respect your word. If you've been waiting for too long before putting an end to the NAP, then it's your fault and you deserve to loose
So : no matter what the context is : a pact has to be respected. If you don't, nobody will trust you later. Period.
And please count -1 yes and +1 no on your poll.
BTW, I am amazed and worried by the number of positive votes...