Why So Serious comes from The Dark Knight in 2008, where Heath Ledger's Joker repeats the line while telling shifting stories about his scars. The phrase was also used in the film's marketing and quickly became the character's most quoted tagline. Clips of the delivery spread through trailers, edits and forums, then later on short video platforms as a shorthand for mock menace. Its mix of comic book history and unsettling delivery keeps it popular for villain tributes, Halloween posts and dramatic meme edits.