Tongue Suicide

A type of suicide that sometimes shows up in eastern works. Need to kill yourself in a hurry without using your hands? Just bite your tongue really hard! It’s like having a stored a Cyanide Pill in your mouth, but you don’t need to prepare in advance. This probably works better in fiction than real life.

An involuntary similar action might be preformed (in fiction) by someone undergoing a seizure, although in this case the concern is being swallowed, not bitten off (although this is a myth https://health.clevelandclinic.org/2014/06/swallowing-your-tongue-and-other-epilepsy-myths/ ).

Anime and Manga

 * Mentioned as a course of action in episode 25 of Kill la Kill.
 * One Piece
 * A slave does this while he is being sold, as he considers slavery a Fate Worse Than Death. He doesn’t die instantly and in fact can presumably be saved if he receives immediate medical attention.
 * After being caught after an escape attempt, Mr 3 suspects he’ll be tortured and says he’ll bite off his tongue.
 * In the 15th episode of the english dub of Samurai Champloo someone is described as having “bit off his own tongue and then killed himself"
 * In Naruto, the character Tsunami volunteers to be taken hostage by Gato’s men and tells them if they touch her son then she’d kill herself by biting her tongue.
 * Misa from Death Note tried to kill herself while restrained. L orders that she be prevented from biting her tongue and Misa's attempt was foiled.