Sell in June and go away
When they say to sell in May and go away, maybe they mean at the end of May.
June is a poor month for equities nearly everywhere. It's the second-worst month on the calendar for he S&P 500 and the German DAX (-2.3% over the past 10 years) while it's easily the worst month for the UK FTSE 100 over the past decade despite a rally in June 2016 after the referendum (the climb in UK stocks that year came because of a sharp fall in GBP).
The rule holds globally but it's not as severe in most of Asia.
With trade worries ramping up and political trouble in Europe, there are plenty of reasons for worry.
One note: the World Cup begins on June 14. That will sap liquidity in the second half of the month and that's usually good for stocks. However, during the most-recent World cup, the S&P 500 gained 1.9% in June but in other years, it's been mixed.
For the UK, however, the FTSE 100 has struggled badly in June in 3 of the past 4 World Cups.