I am sure it comes as a surprise to readers of this blog that a rapper with "ain't" in his vernacular does not understand the nuances of trademark law. The furor began when it was announced that the outgoing Pope Benedict XVI would be called "Pope Emeritus" upon leaving the papal office. As a matter of fact, the rapper does not have "Pope Emeritus" registered with the United States Patent and Trademark Office. He may not even have been able to do so if he tried, because Section 2 of the Lanham Act covering trademark law prohibits registration for marks suggesting a connection with institutions or beliefs.
Without a federal registration, the rapper's only recourse would be common law trademark rights. Even then, his rights would only extend over the geographic area in which the mark was used. Assuming the rapper had a federally registered mark, or had common law trademark rights, and brought an infringement suit he would lose very quickly by virtue of the fact that Benedict does not use the mark in commerce. Unless he goes on large speaking tours, or markets t-shirts or other goods with the mark, then the rapper never would win a suit against Benedict.
If Benedict began doing those things -- using "Pope Emeritus" in commerce -- and if the rapper had a federally registered mark or common law rights, the rapper would still have to prove consumer confusion, which is as unlikely in this scenario as you would expect.
The rapper would have sounded less cretinous if he had threatened a dilution suit, because that does not require consumer confusion. There are two types of dilution: Blurring and tarnishment. But still, dilution requires that the mark be used in commerce to try and promote one's own goods at the expense of the famous or distinctive mark's goodwill. So the rapper would lose here too.
As it is, the only conceivable way that the rapper could bring suit would be to hope that Benedict adopts a confusingly similar website domain name to one that the rapper may already have (I did not check if the rapper has a website). If the domain names would be similar and people trying to visit the rapper's website would instead be directed to Benedict's, then it would at least be somewhat plausible for the rapper to bring suit. He would still lose, because the Holy See would have no bad faith intent to profit, as required by the law of cybersquatting.