Kanye West did not in fact compare his "derrière" to that of his wife, Kim Kardashian, according to a delightful New York Times correction.
Appended to a Grey Lady story about Kardashian's famous backside, the correction reads:
An earlier version of this column was published in error. That version included what purported to be an interview that Kanye West gave to a Chicago radio station in which he compared his own derrière to that of his wife, Kim Kardashian. Mr. West’s quotes were taken, without attribution, from the satirical website The Daily Currant. There is no radio station WGYN in Chicago; the interview was fictitious, and should not have been included in the column. [The New York Times]
The article the Times mistook for real quoted West as saying his "booty is like Michelangelo level."