Tell us what you really think, Carl.

Billionaire shareholder activist Carl Icahn charged BlackRock CEO Larry Fink of running “an extremely dangerous company” in a no-holds-barred debate Wednesday (see photo) that had Fink silently fuming.

Icahn said Fink’s support of corporate CEOs — through an open letter earlier this year in which he told corporate chieftains to resist activists’ pressure to buy back shares — was an “obfuscation” meant as a sales pitch for BlackRock’s exchange-traded funds.

Fink, visibly holding back his anger while Icahn warned of the dangers of the $1.5 trillion junk-bond market, finally got a word in.

“Carl, you’re a good investor, but you’re wrong a lot,” he said. “Your characterization of ETFs as the issue is flat-out wrong.”

Fink said that BlackRock sides with activists about 45 percent of the time — but apparently not that often with Icahn. Icahn said BlackRock had sided with him on only two out of 12 deals.

The two men sparred at Institutional Investor Delivering Alpha’s conference in Midtown — aired live on CNBC.

When asked if Fink considered Icahn a good activist, he demurred, saying, “You’re a good person.”

Icahn returned the left-handed compliment by saying it was BlackRock, not Fink, who is dangerous. “He’s a good guy,” Icahn said of Fink.