Delulu comes from delusional and spread through K-pop fandom slang online in the early 2020s, describing fans who jokingly believe an unlikely romance or meeting could happen. Adding sekali, the Indonesian and Malay word for very, gives the phrase a local twist popular in Southeast Asian chats. Shared as a short WhatsApp audio, it moved beyond fandom into everyday teasing about money, exams, and crushes. Its brevity and familiar slang keep it reusable as a friendly reaction clip.