Suicide

From WoWWiki

Committing suicide by using a self-damaging ability to kill your character counts as a player-caused kill - it does not have the -10% durability penalty attached to it.

This does not apply to dying from a hazardous environment, such as standing in fire, swimming in lava, or jumping off a cliff.

Suicide by spells/skills

Divine Intervention: When protecting someone with this spell, the Paladin automatically dies, without losing durability.

Hellfire: The Warlock ability Hellfire does not reduce durability when it kills the caster.

Seal of Blood / Seal of the Martyr: Dying from these Paladin spells count as a suicide.

Shadow Word: Death: Dying from this priest ability will not reduce the caster's durability.

Suicide by items

[Skull of Impending Doom]: The item Skull of Impending Doom does not reduce durability when it kills the user.

[X-52 Rocket Helmet]: Dying from the damage received upon activation of the X-52 Rocket Helmet won't reduce durability; however, death by falling damage after it has been activated will.

[Crystal of Zin-Malor]: Alliance only. Ideal for canceling flight paths. This trinket will drain health and mana until you are dead or you unequip it.