The small date is based on the system date format: it cannot be formatted by code. Try this:
- Open the control panel, find the regional settings ("Region and Language" in Win 7.)
- Change the short date format to something unusual, such as the ANSI format (yyyy-MM-dd). Save changes.
- Run your app, and look at the date format on the drop down calendar.
In short, you can't get there from here, unless you want to build your own calendar control from scratch.