"I know you never liked me Mr. Secretary-General – well, I never liked you, either," said Sha Zukang as Mr Ban looked on, smiling and nodding awkwardly during the 15-minute toast attended by the UN's top brass.
Mr Sha, who was appointed the UN undersecretary general for Economic and Social Affairs in 2007, also made no secret of his fractious relationship with Mr Ban, although did say he'd grown to respect the South Korean.
"You've been trying to get rid of me," said 62-year-old Mr Sha. "You can fire me anytime, you can fire me today."
Later in his impromptu speech Mr Sha turned to an American colleague, singling out Bob Orr from the executive office of the secretary-general.
"I really don't like him: he's an American and I really don't like Americans," he said.
A second senior UN official who was at the dinner said: "It went on for about ten or fifteen minutes but it felt like an hour."
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