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A candidate for mayor of New York who was mocked by Anthony Weiner as "grandpa" at an AARP forum said today that their confrontation began when Weiner "slammed me a couple of times on my chest."

Weiner acted "like some punk challenging me," George McDonald said today.

Weiner, 48, and McDonald, 69, became locked in a tense exchange Tuesday night before the AARP Mayoral Town Hall.

"Last week at a forum I had called into question Weiner's character and experience and judgment as a legitimate issue in the campaign; I guess he didn't like that very much," McDonald told ABC News. "He came up behind me and slammed me a couple of times on my chest as a greeting."

"I've never greeted anybody like that and I've never had anybody do that to me," he said.

The exchange, caught by NY-1 on camera, shows the two men just inches apart arguing.

"Keep your hands off me," McDonald told Weiner. "Don't put your hands on me ever again."

"What's going to happen if I do," Weiner countered. "You're a tough guy now?"

Weiner then said McDonald had "anger issues," which McDonald immediately denied.

"But you do, grandpa," Weiner insisted.

In an interview with WWRL radio station this morning Weiner said he used the word "grandpa" because McDonald always talks about his granddaughter on the campaign trail, according to the New York Post.

"He talks about his granddaughter in every answer on the campaign trail," Weiner said.

Weiner's campaign did not respond to an ABC News request for comment.

McDonald said Weiner has not offered an apology, and even if he did "it wouldn't mean anything."

"I'm not his grandpa, am I? And the way that he said it, believe me, he wasn't being nice to me," McDonald added. "I don't consider myself a senior, an old person. I came into this race and still have a lot of vigor."

The "grandpa" crack is the latest moment to rock Weiner's campaign, already struggling to overcome the latest revelations of his sexting and his campaign spokeswoman's crude description of a former intern who wrote a tell-all about the campaign.

Women and seniors are routinely key voting blocs and who turn out in strong numbers. According to the AARP, 50 percent of New York voters are expected to be members of their organization.

"AARP found some of yesterday's comments regarding age unfortunate, especially at a time when, according to a new AARP survey, nearly one quarter of New York's 50+ voters say they or a family member have experienced unwelcome comments about their age and nearly half are concerned about age discrimination," Beth Finkel, state director of the AARP New York, said in a statement. "A person's age should not be a factor in politics, or anything else."