After being mocked at prime minister's questions (PMQs), when David Cameron angrily told him to "put on a proper suit, do up your tie and sing the national anthem", Corbyn today appeared with an open-necked shirt and his tie hanging loose as he attacked bankers over the financial crisis.
The BBC's Norman Smith described it as a "casual look":
The move annoyed some, who claimed that, speaking to members of the British Chamber of Commerce, he had the "look of the perennial school rebel who was accidentally made a prefect".
Many watching the key speech, which blamed New Labour's "soft touch" financial regulation that created the conditions for the 2007/08 financial crash, were frustrated at his unbuttoned shirt and loose tie.
But others ignored Corbyn's undone top button and instead praised him for the content of his speech.
One eagle-eyed hack, Jason Keen, spotted a small but significant change in the speech distributed to journalists beforehand and what Corbyn actually said.
"The New Labour approach was to opt for 'light touch regulation' of finance - and then sit back and collect the tax revenues."
"The political consensus at that time was to opt for 'light touch regulation' of finance - and then sit back and collect the tax revenues."
After the long address, Corbyn was asked for his "elevator pitch".
In response to the Labour leader saying it depended on how long the lift journey was, the Chair quipped: "Usually short."