One word describes how Jay-Z feels about the rape allegations against him … “upset.”

In fact, the music mogul’s so mad, his attorney, Alex Spiro, gave a fiery speech Monday invoking that word multiple times in regards to the new lawsuit against his famous client.

Spiro told a roundtable of reporters at Roc Nation headquarters in NYC that Jay feels the suit makes a mockery of the justice system because of what he calls baseless claims made by his accuser.

Jay-Z and Diddy are being sued by an anonymous female accuser who claims the rappers drugged and raped her at a party following the 2000 MTV Music Awards when she was just 13.

Spiro says Jay-Z is also pissed that Beyoncé, Blue Ivy and the rest of his family has to deal with these false allegations. Furthermore, Jay’s angry the suit “distracts and dissuades real victims from coming forward.”

And Spiro doesn’t blame Jay for being so upset … he says Jay has nothing to do with Diddy’s federal criminal case, denying all speculation linking him to it. As you know, Diddy has been indicted on federal charges including racketeering, sex trafficking and other serious offenses.

Jay-Z has vehemently denied the allegations, called the lawsuit a “blackmail attempt” and fired back at the attorney who brought the suit, Tony Buzbee.

In a statement to TMZ, Buzbee responded to Spiro comments at the Roc Nation presser, telling us … “I’ve been representing victims of sexual assault for many years. I’ve seen what they go through when they make allegations against powerful people.”

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He went on … “Typically the defense is to attack the alleged victim. Mr. Spiro has decided to attack the alleged victim’s lawyer. But, I’ve been attacked before and won’t be bullied. As for his client’s nonrelationship to P. Diddy, I won’t comment on that.”