Martin Shkreli doesn’t save his vitriol just for the internet, a Brooklyn courtroom heard Monday.

“Do you know how I know you’re an incompetent idiot?” the pharma cad once wrote to an accountant who was attempting to reconcile his company’s messy financials.

The 34-year-old penned the venomous email after threatening to sue financial firm SEC Solutions Group for taking too long to untangle his company’s long-overdue expenses.

Yet jurors in the former Retrophin CEO’s securities fraud case won’t get to hear the zinger because Brooklyn Federal Court Judge Kiyo Matsumoto agreed with defense lawyer Marc Agnifilo that the exchange would only serve to further “disparage” Shkreli’s character.

“The only reason they want [the email] in [evidence] is that it makes him look terrible,” Agnifilo successfully argued.

Accountant Corey Massella testified Monday that his firm SEC Securities, which would later become Citron Cooperman, eventually resigned from a contract with Shkreli’s pharma company because they found the loudmouth to be “unreasonable and rude.”

After they resigned, Shkreli fired back in an email May 8, 2013: “we do not need your firm’s ‘help.’ Your firm has done an awful job.”

The defense team said the despised pharma bro only acted out because the firm was taking too long to complete the work.

Shkreli — who has been kicked off Twitter multiple times for acting out online — faces up to 20 years behind bars for allegedly orchestrating an $11 million Ponzi scheme.

Prosecutors allege Shkreli used his hedge fund, MSMB Capitol, as a piggy bank to fuel his burgeoning pharmaceuticals company, Retrophin, without investors’ knowledge. He purportedly then paid off lenders with Retrophin funds, without the consent of the company’s board members.

Other e-mails that surfaced in court Monday showed nastiness runs in the family. Shkreli’s sister, Leonora Izerne, who worked for him, told the accountants they did the “sloppiest work I’ve ever seen in my lifetime.”