For example, with a linked list, clearing the list is quite simple (and O(1)):

• Set the pointer to the first element to null.

However, someone I know managed to write it in O(n^2):

• While the list's number of elements is greater than zero.
  • Find the value of the last element in the list.
  • Remove that value from the list.

Ben L.:

However, someone I know managed to write it in O(n^2):

Extra bonus points if he then stores the discarded elements in another list, sorts them, and never uses them anymore. 'Cause that's how we keep selling faster processors and memory.

 Of course, there has been extensive research on this important topic: Pessimal Algorithms and Simplexity Analysis

OK, my favorite function is F(x) = 1. That's O(1). How on earth could I make it O(N^2)?? Hmmm... <Furrows eyebrow>

G(x) = 
  For 1 .. x:
    For 1 .. x:
      NOP

  return F(x)

What a fun and interesting challenge! Please keep posting more creative challenges!

 How do you expect us to beat the recursive whitespace removal algorithm featured on CodeSOD?