Clawing At Own Throat

Human fingernails can be remarkably powerful. They assist grip, and protect the soft skin under them.

Unfortunately, they can also be turned into a tool for Self-Harm.

Scratching one's throat is often the result of Sanity Slippage and is often done in an absent minded way. The character scratching their throat may have an unfocused gaze or Hidden Eyes. Their voice may have dropped to a monotone level, if the character is still capable of talking after causing a lot of damage to their throat.

If the character is in serious danger of killing themselves, there will always be blood.

Clawing your throat would cause a lot of damage, but is a very slow method of suicide, so suicide by clawing the throat is not very common. Yandere characters often do this, but rarely end up dying from it. This trope is almost always played for drama, and is frequently a major source of Nightmare Fuel.

Lastly, it's not always played for self-harm: It's also a frequent reflex for characters that are strangled or force-choked.

Examples of Clawing At Own Throat include:

Anime and Manga

In Higurashi no Naku Koro ni, advanced stages of the Hate Plague infection manifest themselves in the infected clawing at their own skin, particularly the throat. In Onikakushihen, Keiichi kills himself by clawing at his throat after killing Mion and Rena. In Tsumihoroboshi, Rena starts to scratch at her own throat but Keiichi manages to stop her from killing herself.

Film

One of the Final Destination movies has this because the person gets a rope wound around their neck and is clawing at their throat to try to get it off.
A character is manipulated into killing herself this was Hellraiser: Hellworld.

Literature

In Mother Hitton's Littul Kittons the terminal madness the titular planetary defense system induces in intruders makes this the least you do to yourself.
Robert Sheckley's story "The Humours", later expanded into the novel The Alchemical Marriage of Alistair Crompton, has the protagonist try this upon realizing that the recovered portions of his personality don't integrate into his own - rather, all of them together reintegrate into something new.

Video Games

The suicide sequence in Call of Cthulhu: Dark Corners of the Earth seems to imply that the player character strangles himself.