Well, the British economy is sure to take a hit and go through a small recession. Nevertheless, if there is a silver-lining, this is the first time in world history in which a nation left a free trade zone, and it could provide us quite the academic case study for its effects.
Still stupid. The real effect is that tariffs that were suspended due to the agreement will kick back up, British goods and services will be more expensive and harder to sell in Europe and European goods sold to Britons will be more expensive (for which Britons will bear the cost). Good news though, at least it shows that every nations has it's idiots, so maybe European wankers can get off of America's back.