After destroying arch-rival Brendan Hansen for the second time in four days to win his second gold of the Athens Olympics he told the Americans: "Now keep quiet!"
Kitajima stormed to the 100 metres breaststroke title at the weekend but was angry at American accusations that he had used an illegal dolphin kick at the start of the final.
That bottled-up frustration exploded on Wednesday when the 21-year-old stormed to victory in a grudge 200 final, winning in an Olympic record of two minutes, 09.44 seconds.
"That talk about the kick just motivated me all the more to stick it to them," said Kitajima, who became the first Japanese swimmer to win two gold medals at a single Olympics.
"They can stop talking now."
Kitajima, a university student in Tokyo, began swimming at three when his father used to throw him into a pool as punishment for being naughty.
On Sunday, he became the first Asian man to win an Olympic swimming medal since Daichi Suzuki won the 100 backstroke at the 1988 Seoul Games.
After completing the breaststroke double, Kitajima was splashed across the front pages and back pages of the Japanese newspapers on Thursday.
"King Kitajima," "Demolition Man" and "He said it, He did it," were just some of the headlines, while even the financial daily Nihon Keizai Shimbun ran Kitajima on its front page.
"There was a lot of pressure on me but I swam the perfect race," said Kitajima, who also won both events at the 2003 world championships in Barcelona.
His coach, Norimasa Hirai promised Kitajima would be hungry to defend his Olympic titles at the 2008 Beijing Games.
"Athens has been the perfect realisation of his talent," he said. "Watch out Beijing!"
