Delet This, often intentionally misspelled and accompanied by a reference to or a photograph of a gun, is a copypasta used on message boards and comments systems to threaten, often ironically, that the original post is too extreme.
While telling someone to “delete” a post is not new, the specific spelling seems to result from a video of a Gary’s Mod game where a player was “buried alive” by another player. Knowing that the player burying him is recording the game, the buried player shouts “Delete this!” repeatedly in the recording. The video was originally posted at a longer length and then removed; the version below was posted on January 4th, 2014, and has received over 264,000 views since.
It’s unknown when the spelling became modified, although comments with the modified spelling began appearing on the YouTube page itself in early February, 2016. Around the same time, the spelling began to come into fashion as a copypasta style comment on Weird Facebook. While Facebook does not allow comment searching in general, the first searchable use of the phrase as a post title appears to be from the Weird Facebook page “Do Androids Dream of Electric Memes?” which posted it along with a close-up portrait of a man wielding an airsoft gun.
Delet this has become especially popular in several Weird Facebook groups, most notably Simpsons Shitposting and Watermelon memes. In Simpsons Shitposting, it is used both as a copypasta comment and as a way to indicate that someone should be banned; in Watermelon Memes, the idea of delet this has turned into a cinematic event. There, the phrase has been remixed into film studio introduction sequences for dramatic effect.