Bonfire Of The Vanities
A “vanity” is some physical object that’s considered sinful or promoting of sinfulness (e.g. alcohol, pornography). So a “bonfire of the vanities” is a burning of these objects as a symbolic act to promote holiness and rid the world of temptation.
The original “bonfire of the vanities” was an actual event in 1497 where supporters of a Dominican preacher burned things considered immoral. From Wikipedia:
The focus of this destruction was on objects that might tempt one to sin, including vanity items such as mirrors, cosmetics, fine dresses, playing cards, and musical instruments. Other targets included books which Savonarola deemed to be immoral (such as works by Boccaccio), manuscripts of secular songs, and artworks, including paintings and sculpture.
The phrase is more commonly known as the title of the 1987 novel by Tom Wolfe, and a 1990 movie starring Tom Hanks.
Why I Looked It Up
A book about the history of money referred to the original 1497 event and noted that the mob also burned bank records of the Medici family of Florence, Italy. The book notes that the instigating preacher blamed the Medici family for a host of problems.
Postscript
Added on
In The Swerve: How the World Became Modern, the original event is described:
As the fifteenth century neared its end, the Dominican friar Girolamo Savonarola ruled Florence for several years as a strict “Christian republic.” Savonarola’s passionate, charismatic preaching had provoked large numbers of Florentines, the elite as well as the masses, into a short-lived but feverishly intense mood of repentance. Sodomy was prosecuted as a capital crime; bankers and merchant princes were attacked for their extravagant luxuries and their indifference to the poor; gambling was suppressed, along with dancing and singing and other forms of worldly pleasure. The most memorable event of Savonarola’s turbulent years was the famous “Bonfire of the Vanities,” when the friar’s ardent followers went through the streets collecting sinful objects – mirrors, cosmetics, seductive clothing, song-books, musical instruments, playing cards and other gambling paraphernalia, sculptures and paintings of pagan subjects, the works of ancient poets – and threw them onto an enormous blazing pyre in the Piazza della Signoria.