Worst case for QuickSort - when can it occur?

Question

When analyzing QS, every one always refers to the \"almost sorted\" worst case. When can such a scenario occur with natural input?

The only example I came up with is

Answer 1

I believe that the worst case for quicksort depends on the choice of the pivot element at every step. Quicksort has its worst performance, if the pivot is likely to be either the smallest, or the largest element in the list (e.g. the first or last element of an already sorted list).

If, e.g. you choose the middle element of the list, an already sorted list does not have the worst case runtime.

So, if you suspect your scenario is likely to a bad case scenario for quicksort, you can simply change your choice of pivot element to make quicksort perform better.

Note: I know, that this did not give more example of real world occasions for quicksort worst cases. Examples of this depend on the implementation you are working with.