Bring a blonde
Preferably with a fat ass who can sing a song

Meaning

There are several things going on here with this line:
Jay alludes to the following:

“It ain’t over ‘till the fat lady sings”, as in opera.
“Bringing a blonde” seems like a Sinatra move (could refer to Marilyn Monroe, with whom Sinatra was rumored to have had an affair)
Jay-Z’s girlfriend Beyonce is blonde, famous, has a fat ass..but it’s not the same
A critique of how rappers nowadays are doing songs with popstars, and change the style of production just to sell more records. The line after this one shows that’s “not politically correct”.

Remember, Autotune is not the only thing he is criticizing; it’s mainstream rap too!

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