My ideas and my conclusions:
A vault that slowly leaks natural gas into the rooms, which all have airtight seals. Which would make cooking dangerous, but wouldn't kill everyone in the vault. The food dispensers would only dispense raw food. Seal the vault for 100 years.
My conclusions: The people would probably have better constitutions, though they would get sick easily from eating raw food, and from the low levels of oxygen. There would be very few fights involving guns or explosives, as they would set off the gas.
Also, a vault that would slowly fill up with water, until there is very little room left to breathe, but still a little. For extra evilness, have the temperature in the vault be higher than 100 degrees farenheit (about 38 degrees celsius, if I am correct.)
My Conclusions: A lot of things would be very difficult, especially things that involve going down to the lower levels. People would probably get sick easily, and all die off due to the lack of proper waste disposal.
A vault filled with extremely bright lights (ie: brighter than sunlight), and very clean, shiny walls. All terminals would be have very low screen brightness.
My Conclusions: People would have serious eye problems, and using terminals would be nearly impossible due to glare.
A vault in which almost all objects are sharp, or have extremely rough surfaces. All food would come on metal skewers. Drinking glasses and bottles would be very thin, brittle, and prone to breaking. Have very few medical supplies (about enough for half of the population, if the vault wasn't a death-trap, for extra evilness, have twice as many other forms of medicine [ie: vaccine] and very few bandages, disinfectants, antiseptics, pain relievers, et cetera), no firearms or explosives, but a large amount of sharp objects such as knives.
My conclusion: People would get cut, and fight over the medical supplies, with knives, and maybe a few bottles too.
A vault which has no furniture in it, no radio, no entertainment tapes, and no intra-vault mail. People would not be allowed to take personal items in with them. The jumpsuit dispensers would be capable of producing a lot more jumpsuits than normal, and there would be a large supply of needles and thread.
My conclusion: People would socialize with each other (the old fashioned way) for fun, and makes stuff out of jumpsuits for fun and comfort (ie: make a pile of jumpsuits to sleep on) and maybe a few would make things such as tapestries, quilts, or rugs by sewing them together. Or perhaps they would just kill each other for fun, stab each other with needles, vandalize the place, or strangle each other with the jumpsuits. Either way...
A vault with no guns, absolutely no guns, and no batons. Security guards would instead be issued land mines and grenades, and ordered to kill people even for minor crimes. There wouldn't be enough supplies for everyone, only the armouries/armories have locks, and also for extra evilness, all medicines will contain significant amounts of stimulants (so, say, if a person got injured, and took some of the medicine, they would be much more likely to attack things.) For even more evilness, give higher ranking members of the security guards missle launchers, and the authority to kill anyone that displeases any of them.
My conclusion: They'll need a mop...
I also came up with, what in my opinion is a better, more sadistic idea, but it is potentially politically inflammatory, so I am not going to post it.
Anyway, now I feel like I need to give bottles of purified water to beggars in order to regain a good, or even neutral karma level, or kill evil people, and sever their fingers. (I was just trying to say "I feel really evil now" in a clever way, I don't think it worked.)