When you 'darn' clothes, you fix a hole in it by putting threads across the hole. Then, if another hole appears you have to darn it again! Now most people just buy new clothes if there is a hole in their clothes. Poor people will still fix their clothes once, but it means you are very poor indeed if you have to fix or darn your clothes twice! It used to be more common to fix your own clothes but now clothes are so cheap because they are made in 3rd world countries where they have low wages, so everyone can afford to buy new clothes whenever they want.

It means that the items were mended twice because the holes had re- appeared.

"Darn" here is a verb meaning to repair by stitching with thread. If something was repaired twice in such a way, it would reflect a poverty-stricken situation.

Thanks everyone for your comment!