As someone pointed out above, pesticides are (were) a popular method of suicide in certain countries but that has more to do with accessibility and by no means represents it being a pleasant death. Indeed, I have been in life-threatening situations in which despite being suicidal I have actively saved my own life - not because of any 'survival instinct' but to avoid an unplanned and unpleasant death.
Also rat poison. It causes rats to bleed internally. It also causes birds and wildlife to die if they eat the dead rats.
Nasty business. I prefer a trap box. One must be careful with pesticides though. A little off-topic, but I remember a close friend of mine and terrible arachnophobe asked for my advice on ridding his apartment of spiders. I gave him an industrial insecticide with the caution that he used it on the wall and ceiling junctions and not to spray them directly... Of course, he didn't listen.
Fast forward a few weeks and I get a panicked phone call in the middle of the night, a giant house spider (one of the largest species seen in the UK) has crept into his bedroom; he sprayed it with the insecticide and it "angered" the spider which was now on the warpath running around at great speed in random directions. I calmly explained to him that for a spider of that size, spraying it directly with insecticide would result in it receiving only a small dose of poison, the poison in question being a neurotoxin that at small doses caused hyperactivity and erratic behaviour.
People rarely appreciate the consequences of some of these chemicals. The same applies to chemicals used for suicide in humans, the detergent method for example. It's effective yes, but extremely painful. Likewise, drinking corrosive chemicals such as 'drain cleaner', effective but the pain must surely be horrendous.
I would steer clear of poisons, I can barely imagine how desperate I would have to be to consider such a method. But then again, everybody's circumstances are different.
