Living a life of luxury. There are several theories as to the precise origin of this term and the identity of Reilly (or Riley). The earliest attribution is to a comic song, “Is That Mr. Reilly?” popularized by vaudevillian Pat Rooney in America in the 1880s and describing what Reilly would do if he struck it rich. However, H. L. Mencken said it came from another source, “The Best in the House Is None Too Good for Reilly,” by Lawlor and Blake, popular about 1900. Though the original Reilly is no longer known, the cliché survives.