Can Anyone Truly Be A Pacifist?

In the above video excerpt from AMNESIA to individuals are arguing over whether they should take a gun with them. One believes that since other people are trying to kill them that they should defend themselves, which brings us to the bigger question: Can anyone be truly a pacifist? What I mean is: non-violence has been used throughout the centuries to stand up against things people didn't agree with. Two recent examples in the last 100 years are Ghandi and Martin Luther King Jr. But is there are point where defending yourself is necessary and when should someone do this?