What's torture is your grammar, or lack thereof. *shudder*
CO2 is not harmful, how do you think all of those frozen mouse suppliers euthanize thousands of mice a week? They don't have teams of people sitting there whacking mice all day.
CO2 is pretty quick. It's heavier than air, so it sinks to where the animals are. If you have a non-tight fitting lid to limit the mixing of the carbon dioxide with normal air, it works pretty quickly.
Not to mention CO2 is a heck of a lot "cleaner" than throwing them against a wall or counter. I've seen that result in a mess in the bag before.
I normally just flick mine on the back of the head. Once you learn the right amount of force, it goes quickly. But I'm not going to do more than 10 at a time if I can help it. Just takes too long.
Pinks and fuzzies are smother resistant, so gassing is not going to work as well for them. I usually just freeze those straight, they don't last but a few mins before they expire. I put them in old ice cube trays to keep them separate and from huddling for warmth, works like a charm. Although most of mine are fed live to save the time and trouble.
And Owen, before you go recommending things next time, I think it would be wise to do some research before espousing your "knowledge". CO2 is generally accepted by several institutions as a humane method of euthanasia.