I ain't sure on how this site works, but here is one of my suggestions.
How about the ability to shoot yourself, so you won't zombify, but die? I'd imagine this would work by holding right click on yourself and choosing "shoot yourself" or something along those lines. This would instantly kill you, but you won't zombify, as you destroyed your own brain. While this should be in both solo and multiplayer, I can see it being used more in multiplayer to save the others from having to kill the zombified player themselves. The player doesn't have to be infected to be able to kill themselves, instead they can do it as long as they have a gun.
Something that could spice this idea up (and really set the vibe and tone for the game) would be a "failure" mechanic to this. Basically, the more healthy and happy you are, the bigger the chance of not "going through" with shooting yourself. As your sanity and happiness lowers, however, the likelyhood of the character "going through" with it will increase. Basically, the more depressed you are, the more likely you are to actually succeed in ending your life.
