When would you say 'no' to authority?

The Milgram experiments are famous for demonstrating how people will, under the right circumstances, carry out violent acts due to authority. (Details here: http://en.wikipedia.org/wiki/Milgram_experiment)

But what of the people who refused to go along with the elaborate experimental charade. I have just been pointed towards this site (thank you 'the psychologist' January 2010) which has a first hand description by someone of why they refused to administer more pain to the 'subject':

Then the most disturbing part of the entire experience occurred: The professor brought in the learner and I was flabbergasted. His face was covered in tears and he looked haggard. He offered his hand and thanked me for stopping the experiment, saying that the shocks hadn't really hurt but anticipating them had been dreadful. I was confused as to whether he was in earnest or acting. I left unsure, and waited outside for the learner so I could discuss it with him. After about a half hour he had not appeared, and I was convinced that he was an actor and that my suspicions about the experiment had been correct. The report that I received confirmed that the experiment was designed to see how far subjects would go in obeying orders to administer pain to others. It had arisen out of the desire to understand the widespread obedience to horrendous and brutal orders in Nazi Germany. The report also confirmed that the professor and learner were indeed actors, although not professionals — and I have always thought that they deserved Academy Awards anyway...

It is worth a read! http://www.jewishcurrents.org/2004-jan-dimow.htm

And this got me to wondering - when would I refuse to go along with authority - under what conditions would I say 'no'?

How about you?