Name Badge Date Format
Ok, I found it.

In CRM/Badge/BAO/Badge.php around line 101 it says:

// hack to fix date field display format
if (strpos($element, '_date')) {
  $value = CRM_Utils_Date::customFormat($value, "%B %E%f");
}


So I just re-hacked the hack and replaced "%B %E%f" with "%e %B %Y".