The line comes from Batman Returns, the 1992 film in which Danny DeVito plays Oswald Cobblepot, better known as the Penguin. In the film the Penguin is a grotesque, scheming villain whose polite manner often hides a threat, and that contrast is exactly what makes a simple instruction to relax feel unsettling. Clipped from the movie and shared as a short sound, it has found a second life in memes and video edits, where creators use it to undercut tension with dark humour rather than to quote the plot directly.