Bloomberg isn't using hyperbole either.

When the history of democracy in this era is written, these two boneheaded decisions will likely stand as the worst made by the voting populace of any major industrialized nations. Both the UK and the USA effectively shooting themselves in the foot with ramifications for decades to come.

Source: The Guardian

Michael Bloomberg, the billionaire media mogul and former mayor of New York, has said Brexit is the “single stupidest thing any country has ever done” apart from the election of Donald Trump as US president.

Bloomberg argued that “it is really hard to understand why a country that was doing so well wanted to ruin it” with the Brexit vote, in a series of outspoken remarks made at a technology conference in Boston a fortnight ago.
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Bloomberg first made the comments about Brexit at the little-reported HUBweek conference in Boston less than two weeks ago – and then repeated his quip about Brexit and Trump at an event in France on Monday.

“It is really hard to understand why a country that was doing so well wanted to ruin it,” Bloomberg said of Brexit. “It was not a smart thing to do and getting out of it is going to be very difficult and is going to be very painful. It will hurt industries. People are already taking space in other cities over there [Europe], us included.”