Shark Tank's Robert Herjavec: What it's like behind the scenes

Shark Tank judge: No one cares about your mistakes

Out in the wild, when a shark flashes his teeth with a pearly smile, it's probably because he's about to attack.

Things may not be that different on the set of "Shark Tank." In a Reddit "Ask Me Anything" forum, "Shark Tank" judge and serial entrepreneur Robert Herjavec gave a glimpse into what goes on behind the scenes when the judges compete for and debate big business deals.

"We have a very powerful relationship with our own money so ya, it gets serious," he wrote. "Tension is very real."

Robert Herjavec
D Dipasupil | Getty Images

Herjavec has found himself in multiple heated exchanges with fellow judges, most notably when he and judge Lori Greiner went head-to-head over a $40,000 potential investment in Scholly, a scholarship finder app.

It ended with Herjavec getting out of his chair saying, "You're really p-----g me off right now. I'm going to say something rude to you, and I don't want to say something rude to you, so I'm just going to go."

When asked on Reddit whether Kevin O'Leary or Mark Cuban would win a fistfight, Herjavec replied "Herjavec."

Robert Herjavec
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Herjavec also threw some shade at O'Leary, nicknamed "Mr. Wonderful," after an exchange between O'Leary and Barbara Corcoran.

"Mr Wonderful wouldn't say he's cranky. he would say he speaks the truth all the time ... so yes - he's that Cranky. all the time," he wrote.

So what is one thing Herjavec would change about the show? "Kevin's suits. i'm so tired of all black suits," he wrote.

Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."