|EVALUATION OF SELECTED METHODS
Shooting: Assuming minimal knowledge of anatomy, sufficient caliber, and a steady hand, it's quick and certain alright, and probably painless too, though it's hard to be sure. Discreet? Well, once you have the weapon in hand, no one can stop you, so the question is moot. Accessibility varies widely: obviously in the USA it's more accessible than we'd like, but in the UK for example it could be nearly impossible. Safety depends heavily on the choice of location. All in all, it wouldn't be such a bad method, if it didn't make such a terrible mess.
Hanging: Not very quick or certain, with a decent chance of mere injury. High marks for accessibility, but unfortunately the risk of detection is also high, because hanging takes a while, unless you manage to break your neck, which is relatively hard to do. Most people probably wouldn't consider hanging painless, but obviously there's a minority who enjoy this type of thing (see the classic British film "The Ruling Class" for example). No one who has ever seen a choking victim would describe this method as "tidy".
Driving: A fine example of an unsafe method. What did all those total strangers ever do to you? Cars are accessible enough, but collisions have surprisingly low fatality rates, and usually aren't quick, painless, or tidy.
Jumping: Fairly quick, depending on the height, but not all that certain. You'd be astonished at how many people have survived outrageous jumps. San Francisco's Golden Gate bridge draws jumpers from all over the world, but the locals are hip, and many people are stopped in the act. This method has a high probability of a making a truly disgusting mess.
Slashing: Unless you're a Marine, you probably don't have what it takes to slice yourself deeply enough to do the job. There's a fine line between self-mutilation and an actual suicide attempt. In most cases this method is just a cry for help. Straight razors are accessible enough, but this method is definitely not painless, certain or quick. It might look glamorous in the movies, but don't be fooled: a bathtub full of blood is not a pretty sight.
Drowning: Not particularly discreet except in very isolated areas, and even then it's advisable to do it at night. If you're a good enough swimmer to get far enough out, it's fairly certain, especially in frigid water, but it's not quick by any means. By some accounts it's moderately painless, but where your bloated corpse will wind up, and to what extent it will be chewed, is another matter.
Freezing: If you can manage to get above the timber line in winter and get naked, this method has a good chance of success, but be careful to take public transportation. People have been rescued by over-zealous park rangers who were tipped off by an extra car in the parking lot. Unless you're in the Arctic circle, it takes a while, but it's relatively painless once you get past a certain point. Accessibility varies widely, but freezing gets high marks for safety and tidiness, and is ideal for nature-lovers.
Overdosing: This is a huge topic, and beyond the scope of this text. Suffice it to say that the lethal dosage for a given substance depends enormously on the individual. In many cases the odds of organ damage are much higher than the odds of death. Many attempts fail due to the human body's annoying tendency to vomit when poisoned. Most experts recommend combining drugs with alcohol and a garbage bag over the head, secured with an elastic.
Nitrous Oxide (NO2): When properly applied (using a mask or a garbage bag), it's astoundingly quick and certain, and downright pleasurable. The hard part is getting the stuff. It takes a lot of whippets to fill up a garbage bag, and it's difficult to purchase a tank unless you happen to be a dentist.
Oven Gas: This method is totally unacceptable, due to the obvious danger of blowing up total strangers.
Car Exhaust: This is a fine example of a method that's reasonable in theory but rarely works out in practice, because it's so hard to do discreetly. A tube from your tailpipe to your car window is bound to attract attention. Run your engine in your garage long enough, and you'll be visited by a nosy neighbor. Sure it's painless, but failure means brain damage. The active ingredient (carbon monoxide) is effective, though other gases are much better (see below); it's the delivery method that's unacceptable.
Carbon Monoxide: This gas binds to your hemoglobin better than oxygen. Your body thinks it's oxygen, and you breathe normally, except that you die. It's not as much fun as nitrous oxide but it's also somewhat easier to obtain. The best way is from an industrial gas supplier but acceptable concentrations can be obtained by indoor use of a charcoal grill. The main problem with carbon monoxide is that it's flammable! It also tends to sink, so it could accidentally asphyxiate your downstairs neighbors. For a demonstration of how to kill yourself with carbon monoxide, see the Jerry Hunt video.
Helium: In addition to being odorless, colorless, and non-flammable, helium is also considered non-toxic, but it's an excellent suicide method; it's as easy to breathe as air, except that your voice becomes high-pitched, and after a few minutes, you become unconscious and die. Helium is used to inflate balloons, and is therefore inexpensive and widely available, compared to nitrogen, or other inert gases (such as neon) which would work just as well. Helium also disperses easily, provided you leave your windows open. Helium is quick, painless, certain, discreet, safe, accessible, and tidy.