The only way I'm going to kill myself in that situation, is if I'm already infected, and I can kill a whole lot of zombies at the same time. For instance, leading some zombies into a trap/explosion radius, etc.
Depends on how much of a puss you are. I'm not a fan of the 'easy way out'. The only reason you should shoot yourself, ever, is if you are infected and a danger to the group you may be traveling with. If I'm able to fight, you bet your ass I'm fighting til the end.
But, on the traps, what is the average time limit you have 'till you secumb. If I had hours I would dig some large pits and fill them with some kind of accelerent, then act like the pided piper and escourt the zed heads the the funeral pire, after that I would just sit down with a live granade, only the pin is out handle is still being squeezed. If it's just a few minutes the I'd sucide bomb as many as I could. Now the whole friend thing, I'd ask them to shoot me when I was a sleep other wise I'd foolisly try to defend my self.
I would never unless It was to avoid a zombie eating me alive. Even if bitten and was able to run away. I'll just turn.......always wanted to see the other side haha. But I would expect anyone that I have teamed with to end me as soon as possible.