Weekend sleeps and an editing question

I have another editing post I want to write, but it's been a series of very long days at the dayjob, and I keep nodding off at my computer. Plus there are sunbeams...

So in the interest of keeping the conversation going, I have a question. What is the hardest thing for you to fix when you edit? A stubborn character? A plot worn full of holes? A descriptive tic you can't stop making? (Like my main character WOULD NOT STOP SHIVERING EVER AHHHH!)

 What makes you bang your head against the keyboard?