IF the criteria is "shockingly losing her title" then I can't imagine that any of the three women offered in vote would be more "SHOCKING" than Lindsay Lohan (assuming she can get/stay clean and sober long enough to pull it off!)
Both KK and Fox clean up nicely and you can almost see them being 'tough enuf' to beat up cute little Miss Johansson...unlike Lohan. So that's why LL gets my vote as "the most shocking" upset.
If you want an "other" - I see Kournikova (or even Hewitt) as being somewhat more shocking than either Kim/Megan (given Anna's "loser rep" and Hewitt's "goody girl" image.
Personally, I'd love to read a story of Charlize Theron taking Scarlett to the woodshed, but that would definitely NOT be an upset - which is the thrust of this thread!