Cotton-picking is an American way of making a feeling stronger when you are annoyed or surprised, as in “Wait a cotton-picking minute!” It is informal, a bit old, and sounds like a parent or an old film, not a school essay. Though actually, the picture behind it is not gentle: for a long time in the American South, picking cotton was hard work done by enslaved Black people, and later by very poor workers. Because of that, some people find the phrase ugly or racist, and some writing guides tell you not to use it. Other Americans still say it as a mild, almost jokey intensifier and do not mean harm. You should know both the everyday use and why it can sting.