Delulu is short for delusional.

My best friend is just as delulu as me. She hyped herself up to think that her situationship was going to turn into a relationship.
History and usage

Delulu can be traced back to K-Pop forums by the K-Pop community in 2014. They used the term "delulu" to describe other fans' beliefs about certain K-Pop stars.The K-Pop community better known as army rides hard for their beloved artists.

Delulu later made its way to TikTok in November 2022 and was used by the mainstream to describe romantic situations or situations completely unrelated to K-Pop. Brands started taking to the term in 2023 and many memes and videos have since been made using the term.