The worst time to trade forex is when there is less activity in the market,that is when there London and European market are closed and other markets like the Tokyo session is relatively inactive.
if a country is has conflict, especially war., it is very terrible and very difficult to analyze the movement of these currencies
the second one if the country disaster. This news like that of Japan some time ago.,
advice: please avoid trading at the moment. because of the price movement away from predictions that have been analyzed
There is no worst time to trade. Different periods just mean different strategies. For instance in non volatile periods you can use bollingers to trade by selling at tops and buying at bottoms... in volatile periods you can use break outs and so on
If your trading not suitable for volatile market , then non farm payroll data is very risky one that coming every 1st friday of the month. It kill many account but some people earning good as well.
As you sow, so shall you reap.
I don't know if it's true but before a few months when it was November and December , my friends told me that end of a year is the worst time to trade in Forex . but i never felt it when i traded in this period , it was as usual for me (I don't know if it was my luck or it's their misunderstanding ) . and i want to agree with forexsage , I do think that different period means different strategy .
i don't trade sideway market, so the worst time for me is when the market is sideway or volatility is low.
thats why i only trade at london and US sessions.