Passing out from breathing pure helium for too long is slightly pleasant and I imagine nitrogen would be similar. Though my friend said my foot was twitching. (I regained consciousness right when he figured out I wasn't joking around and had really passed out.)
In my misspent youth, I was once helping a friend with a project involving a couple of weather balloons full of helium. When he was done and we were cleaning up, I was playing around with breathing pure helium. One breath of pure helium was fine, and I followed it up with a second breath of pure helium, figuring I would feel hypoxia start to set in. It sets in fast and is actually euphoric. I remember saying "whoah" and realizing I was about to pass out, and I remember hearing my head hit the rubber floor I was sitting on. (I did sit down, since I realized there was a danger of my passing out.)
EDIT: I should point out that I used to be in favor of the death penalty, but now feel that it is usually little more than state-sponsored vengeance. I would like to see a cultural shift in America away from all forms of vengeance , and legitimizing vengeance against murders is worse than helping the families of murder victims realize that vengeance is neither necessary nor sufficient for closure.
If we as a society are determined to kill murderers, my experience suggests that breathing pure nitrogen would be one of the least barbaric ways to do so.