Obsessions: #6 "Fifty Shades of Grey"

"Fifty Shades of Grey," the first book in a trilogy of "Twilight"-inspired fan-fiction bondage erotica by E.L. James, became an underground reading obsession for millions of women in 2012. (Rob Kim/Getty Images)

"Fifty Shades of Grey," the first in a trilogy of "Twilight"-inspired bondage erotica by E.L. James, became an underground reading obsession for millions of women. Some called it "mommy porn" (which led to inevitable parodies); hotels in the Pacific Northwest offered "Fifty Shades"-themed "sexy weekend getaways"; and at least one man retaliated against his girlfriend when he discovered she was reading it: He squirted her in the face with a bottle of steak sauce.

The steak sauce assault happened in the U.K., where "Fifty Shades of Grey" has become the best-selling book of all time, according to the London Telegraph. The book recently surpassed "Harry Potter and the Deathly Hallows," selling more than 5.3 million copies.

"The 'Fifty Shades of Grey' phenomenon is perhaps one of the most extraordinary experiences of my entire publishing career," one Random House executive told the paper. "The speed and sheer size of the sales is incredible."