ABC News’ Michael Falcone reports:

CONCORD, N.H. — On the campaign trail on Wednesday, Herman Cain did not miss an opportunity to contrast himself with the candidate he is now challenging for the lead in the race for the Republican presidential nomination — Mitt Romney.

When asked what he thought of Romney’s suggestion at Tuesday night’s debate that Cain’s 9-9-9 economic plan was too simplistic, the businessman turned presidential hopeful called it a “put down.”

“A plan can be simple without being simple-minded,” Cain said. “Someone once said, ‘simplicity is genius.’ I believe that’s why I was attacked so much.”

(Cain said he first heard the phrase, “simplicity is genius” from the son of his campaign manager and chief of staff, Mark Block, who was traveling with Cain on Wednesday.”His son used to be a soccer player and that was a phrase that his coach passed on to them and he passed it on to me,” Cain said.)

“I think that’s what’s driving a lot of people crazy. They keep saying it’s too simple,” Cain said of his economic proposal. “It’s simple, it’s transparent, it’s efficient, it’s fair and it’s neutral. They’re having trouble with that.”

Cain went on to recall the moment when, at the debate, he challenged Romney to name the 59 points of his economic plan.

“His only response had to be, ‘well, you know not everything can be solved simplistically’ — yes it can,” Cain told reporters at the Ninety Nine Restaurant in Concord.

“I used to run places like this,” said Cain, whose career includes stints as the CEO of Godfather’s pizza and as the head of the National Restaurant Association. “I’ve had to count the inventory and balance out the cash register receipts at night. I’ve had to be the last one in the restaurant to clean it up. … I’ve been a hands-on businessman.”

And when it came to Romney’s solutions to getting the economy back on track, Cain continued to extoll the virtues of simplicity.

“His so-called economic plan throws a lot of stuff in there that he’s trying to address. The biggest thing that he doesn’t do is throw out the current tax code. I throw out the tax code right away.”

Cain added, “You start throwing all this stuff in there, you’re going to end up with another 2,700 page bill…they’re not going to read it. So, give them specific, clear solutions for the major issues that we face.”

As Cain continued to hold court in the diner, a reporter asked him to reveal which of his opponents’ attacks at the debate bothered him most. Cain grinned, turned to his campaign spokesman, J.D. Gordon.

“This will probably get me in trouble,” he began, “but as my grandfather would say, ‘I does not care.”

“Governor Huntsman and Representative Bachmann were trying to be cute,” Cain said. “I don’t get upset about that kind of stuff.”

Romney, Cain repeated, “was trying to do a put down.”

“But I think it was the one by Senator Santorum that particularly bothered me,” Cain said.  “Number one, he totally misrepresented the facts.” (Cain said Santorum’s contention that his 9-9-9 plan imposes an 18 percent tax on people was “absolutely wrong.”)

“It’s a package — 9-9-9. What did he try to do? He tried to get the audience to react on each one of those individually,” Cain said. “And it backfired.”