(ABC News)

TRENTON, N.J. - No one would accuse Chris Christie of not telling it like it is, and now the New Jersey governor is telling Mitt Romney that he, too, should be more open.

Admitting they are "stylistically" opposite, Christie told ABC News in an interview at the state capitol that will air Tuesday on "Nightline" that although "he's much more reserved," the presumptive GOP presidential nominee should open up.

"I think he does," Christie said, referring to Romney adopting less of a reserved style. "I think he does, and I think he knows that. I think as time progresses in this campaign, you're going to see him open himself up more and more to the American people, and let them see who Mitt Romney really is, like I've had the opportunity to see. And I think when they do, they're going to like what they see."

Watch ABC News' Jake Tapper's full interview with Gov. Chris Christie on "Nightline" tonight at 11:35 p.m. ET.

Christie is high on most veepstakes lists and in the interview he didn't deny that he has handed over paperwork or his personal documents to the Romney campaign, saying any "phone calls between me and Mitt Romney are between me and Mitt Romney."

"I think any of that stuff is up to the Romney campaign to talk about and not up to any of the individual people who might be being vetted to discuss," Christie said.

Christie said he would "take the call" if Romney picks up the phone and asks him to join the ballot.

"He's the nominee of my party, and if he calls and he wants to talk about that, I'll talk to him about it," Christie said. "But that's up to him, not up to me."

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Christie considered a run himself, but says now he doesn't regret not taking the plunge because he "love(s) this job" and he "didn't feel right about leaving."

He acknowledged that he sat down with his wife Mary Pat and four children before deciding against a presidential run and said he would do the same if Romney asked him to join the ticket. Christie did give some names that he thought would be good choices if he's not on the ballot.

When asked if former Alaska Gov. Sarah Palin would be on that list - the two have not always had the best relationship - he said he hasn't "heard her being discussed this time around."

"I think Gov. [Bob] McDonnell from Virginia is somebody who would be an outstanding choice," Christie said. "Sen. [Marco] Rubio would be an outstanding choice. Sen. [Rob] Portman would be an outstanding choice. Gov. [Tim] Pawlenty would be an outstanding choice. You know, Gov. [Mitch] Daniels would be an outstanding choice. Gov. [Haley] Barbour would be an outstanding choice. All these folks are really good. And I think all could add to the ticket and could help Gov. Romney."

Christie opens up about his 30-year struggle with his weight. Read more here.

Christie addressed a special session of the legislature Monday, but he made national headlines not for the speech, but for calling a reporter an "idiot" over the weekend. Asked if he's ever "concerned" that some of his "rhetoric is too much," he answered plainly: "No."

"I don't worry about that," Christie said. "I'm not monochromatic. You know, I can walk and chew gum at the same time. And the fact of the matter is sometimes to get people to the table, you have to be blunt and assertive, or else they'd all come to the table with the right kind of attitude. You know, you have to read the situation and, and that's part of what leadership is all about. Sometimes people need a pat on the back and an arm around them. Sometimes they need a kick in the rear end. You have to be able to read that; experienced leaders can do that. And I think I have the ability to do that."

He said he doesn't regret calling the reporter stupid because "when someone acts stupid, I'm going to call them stupid."

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Chris Harris from the Bergen County Record asked Christie about state business: whether he was planning on addressing the legislature Monday. Christie said reporters were told to stick to the topic at hand, an emergency at a water treatment plant, and "if you don't have a hearing problem, you should be able to follow the rules. Those are the rules."

"If you don't want to follow the rules, leave the press conference," Christie said. "I mean, I'm not going to put up with stuff where I'm dealing with a serious situation, where people are having a crisis in Monmouth County regarding a lack of water. I'm down there to talk about that. I'm not going to talk about other stuff."

The entire interview will air tonight on "Nightline" at 11:35 p.m.