From Discworld & Terry Pratchett Wiki
One of the more common causes of death in Ankh-Morpork, Suicide on Roundworld refers to the willful and premeditated taking of one's own life. However, the famous Morporkian literalism steps in to expand this definition until it includes not only self-initiated suicides but also those actions that are guaranteed beyond a doubt to result in another being killing the suicidal person in question. Should the Watch conclude that they are investigating a case of Suicide, (suicide with a capital S,) they will tend to wrap up the investigation swiftly and move on to something more important.
Methods of committing Suicide:
- Walking into the Mended Drum and announcing that your name is 'Vincent the Invulnerable' or some-other-such-nonsense works every time.
- Calling a Nac Mac Feegle 'a fairy' will bring about a fairly quick Suicide.
- Shouting "All Gods are bastards!" in the middle of a thunderstorm, whilst wearing copper armour, counts as Suicide.
- Going up to a Witch, werewolf, vampire or Susan Sto Helit, leering, and proclaiming; "I likes a girl with spirit!" is extremely ill-advised, even if, strictly speaking, you're left alive afterwards to ponder the wisdom of your actions, having just slid down the learning curve...
- Unlicensed theft is Suicide. So too is unlicensed assassination, unlicensed fooling and unlicensed 'needlework'.
- Attempting to apply the Marquis of Fantailler rules of pugilism in an actual fight, is a very effective method of Suicide.
- Standing between the parades on Battle of Koom Valley Day/Troll New Year is Suicide, (unless you happen to be Capt. Carrot Ironfoundersson of the Ankh-Morpork City Watch.)
- Swimming in the River Ankh is suicide.
- Fishing in the River Ankh is also suicide. If Harry King doesn't get you for violating his sole right to "waterborne salvage", your catch will be ornery enough to express an opinion about it.
- Calling a dwarf "short stuff," will either result in Suicide, or a sudden lack of leg below the knees.
- Referring to trolls as "stupid rocks" is also a sure-fire way to commit Suicide, as is looking elvish in the presence of dwarves or trolls.
- Stepping on a gnome will generally not result in Suicide, although it has unfortunate consequences for those who do.
- Wielding a flamethrower in the presence of a swamp dragon is Suicide--either due to the dragons, or due to Lady Sybil catching you in the act or finding out about it.
- Attempting to rob the Bucket, in full-view of members of the Ankh-Morpork City Watch and/or take a certain member of the Watch hostage, is Suicide.
- Taking a stroll through the Shades is Suicide, or at least it was until the Watch was brought back up to full-strength. Now, it is possibly only attempted Suicide.
- Attempting to swindle, cheat, rob, or otherwise deceive or harm any member of the Seamstresses' Guild is a Suicide once the Agony Aunts find out. Those who survive are best advised to not complain...
- Being curt, frank or unpleasant to Mr. Jonathan Teatime, before his death, was a method of Suicide.
- Messing with Rincewind is Suicide, (though indirectly,) since The Luggage (or, if you´re lucky, whatever Rincewind´s running away from) will eventually catch up with you. Messing with the Luggage itself is also Suicide.
- Attempting to traffic in Scrape, slab, or any other troll drug is Suicide... once Sgt. Detritus the troll catches up with you, though as actually causing a citizen to commit Suicide in this manner would be classified as "police brutality" and would result in unnecessary paperwork, Sgt. Detritus will probably leave you alive. Probably...
- Staging an assassination attempt on Mustrum Ridcully is Suicide, by way of the two loaded-crossbows he keeps handy on his bedside table or on his person.
- Standing near a Nac Mac Feegle mound with a spade, intent on digging will for the moment, be called Suicide... until a proper name can be invented.
- Devising a zoolological taxonomy for all living-things on the Discworld becomes Suicide when you choose to give Trolls the Latatian classification of stultus saxum, ("Stupid Rocks,") or Werewolves, lupus sapiens ("clever doggies.") Add to this Latatian terms for Dwarfs that translate as "garden ornaments" and Vampires as "bloody undead" then you will have a Suicide-in-the-making.
- Tapping Cohen the Barbarian or any member of the Silver Horde on the back may result in Suicide... or it may just result in the loss of certain popular body parts...
For the Roundworld definition of suicide, see here, but put simply, "suicide," (Latin suicidium, from sui caedere, "to kill oneself,") is the intentional killing of one's self. The most common cause is an underlying psychiatric disorder, such as, but not limited to, depression, schizophrenia, alcoholism and drug abuse. Financial difficulties or other undesirable situations play a significant role in the developing world.
World-wide it is the tenth leading cause of death with over one million people committing suicide every year. It is one of the leading causes of death among teenagers and adults under 35. There are an estimated ten to twenty million failed suicide attempts every year worldwide! That makes even Ankh-Morpork look tame (not considering the population difference...)!
The Discworld definition of Suicide is sometimes used on Roundworld too, as in "Suicide by cop"