The code looks like:

private void DoSomething()
{
List<string> foo = new List<string>();
foo.Add("a");
foo.Add("b");
foo.Add("z");
foo.Add("e");
foo.Add("j");
foo.Sort(new StringReverseComparer());
MessageBox.Show(foo[0]);
}

public class StringReverseComparer : IComparer<string>
{
   public virtual int Compare(string x, string y)
   {
       return x.CompareTo(y) * -1;
   }
}

The framework already has all the relevant comparers for the basic types, so
this isn't something you would normally do for a string collection, but the
point is valid for any generic type.