The line comes from the fictional gangster film watched by Kevin McCallister in Home Alone, where a mobster wishes his victim a merry Christmas before shooting him, and in the Latin American Spanish dub that insult became 'gusano miserable'. The scene was already famous in English as 'ya filthy animal', but the Spanish version took on a life of its own in memes, WhatsApp audios and Christmas jokes across Latin America. It survives because it works in December and all year round as a playful, exaggerated insult between friends.