An audience member ambushed John McCain on Thursday at an otherwise placid town hall meeting in Des Moines, Iowa, with a surprise question about whether he had ever called his wife by an obscene term.

The man stood up and first said he wanted to ask the Arizona senator about a "mental health and mental health care" concern.

"Previously I had been married to a woman who was very verbally abusive to me," the man said. He paused and asked, "Is it true that you called your wife a c***?"

The crowd booed, and McCain responded:

"No, no -- you don't wanna, you don't wanna. You know, it's a great thing about town hall meetings, sir," he said. "But we really don't -- there's people here who don't respect that kind of language. So I'll move onto the next questioner in the back."

Secret Service agents escorted the man out of the building.

The question came out of a new book called "The Real McCain," by Cliff Schecter, that alleges McCain publicly called his wife Cindy that word in 1992. The McCain campaign has called the book "trash journalism" and called the alleged incident a "complete fabrication."

FOX News' Mosheh Oinounou contributed to this report.