KMS is an internet shorthand for kill myself. It is mostly offered as a melodramatic expression of frustration or disgust or a more serious expression of discomfort or sadness. KMS is sometimes brief for kilometers.
Content warning: This article deals with the sensitive topic of self-destruction and an internet culture that, unfortunately, sometimes renders light of it. If you (or anyone you know) are reasoning about attempting suicide, please call the toll-complimentary, 24/7 National Suicide Prevention Lifeline at 1-800-273-8255.