Baking NAN bread correctly is difficult.
Catching turkeys from China is difficult.
to criticize someone for no reason, just to nag at them.
a hardship, big trouble. Not like "Oh, If I fail this test, I'm going to be in big trouble!" こんなん is more like an ongoing hardship, like your parents died when you were young and you had to put yourself through school while working 20 hours a week washing dishes. Also often used in this phrase: 困難の時代 (troubled times)