He later tweeted:
2. Boris Johnson forgot the name of the Tory candidate in a key by-election.
3. Nick Clegg forgot the name of the Liberal Democrat candidate running against Alex Salmond.
The Lib Dem leader was asked by the Press and Journal about his party's hopes of beating Salmond in Gordon, Aberdeenshire. He accidentally referred to candidate Christine Jardine as Justine.
He said: "I was speaking to Justine…" Corrected by the newspaper, he continued: "Christine, sorry, Jardine."
4. Ed Miliband forgot the name of Swindon's Labour leader.
5. Ed Miliband also forgot the names of all three candidates in the 2011 race to be leader of Scottish Labour.
6. George W. Bush forgot the names of several foreign leaders.
7. Diane Abbott forgot Scottish Labour leader Jim Murphy’s name.
Veteran Labour MP Diane Abbott called Labour's high-profile Scottish leader "John Murphy" in an interview with BBC Radio 4 in January.
She was angry about his plan to hire 1,000 extra nurses in Scotland using the proceeds of a mansion tax in the southeast of England. She said: “I’m very surprised John Murphy is making these boasts. I support the mansion tax in principle but there are to big problems."
Murphy hit back: "It’s hard to take this argument seriously. I mean, she didn’t even remember my name at the start of it, and I don’t have to consult Diane Abbott about what I do in the Scottish Labour party."
8. The Indian prime minister forgot David Cameron's name.
9. Barack Obama struggled to remember the name of his vice president's wife.
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The US president just couldn't remember the name of Joe Biden's wife during a speech in 2013. He was trying to praise the efforts of Michelle Obama and Jill Biden to help wounded veterans, but the latter's name escaped him. "Michelle and vice president .... uhh ... the ... uhh ... Joe Biden's wife, Dr Jill Biden," he said.
10. Philip Hammond confused Labour's Liz Kendall with her colleague Rachel Reeves.
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Tory minister Philip Hammond accidentally called shadow care minister Liz Kendall, a fellow panellist on the BBC's Question Time, "Rachel" – confusing her with Rachel Reeves, the shadow secretary of state for work and pensions. In a nod to the Tories' apparent woman problem, Kendall hit back: "I know we all look the same."