The phrase comes from Moroccan Darija, where 3lach means why and tekdeb means you are lying, and it has travelled online as a compact reaction sound rather than as part of a known song, film, or television scene. Its appeal is its bluntness: in a few syllables it questions someone's honesty without needing a longer explanation. That makes it easy to reuse across languages, since the tone and context do the work even for listeners who do not speak Darija. Short reaction clips like this stay popular because they can punctuate a joke instantly.