Looks like you need to improve your India vs Sri Lanka skills too 
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Even though this topics is basically the same as Hardest countries? , I will oblige: Out of the countries that currently give me the most headache, Russia is the one that forces me to guess randomly within the country the most. But I also do not know much about Russia, yet, so that is expected.
However, the Philippines are a strong contender for the most annoying country to guess within, though - or when I guess Indonesia when it is actually Philippines.