The phrase is Turkish slang, with lan used as a blunt way to address someone and namert meaning a coward or dishonourable person. As a short audio clip, it has circulated mainly as a reaction sound for missed calls and ignored messages, rather than as part of a widely identified film, show or song. Its appeal comes from the directness of the wording and the raised, impatient delivery, which translate easily even for viewers who do not speak Turkish. That simplicity has kept it useful in short-form edits, where a single shouted line can carry the whole joke.