In any language I've ever used, manipulating dates, times, datetimes...always is a big pain
I'm no expert in PHP, but unless DATE_FORMAT is some PHP constant (which it could be, for all I know) then you need to actually enter the format that you want as a string. The PHP reference for the date function is here.
An example:
<li><strong>Date Joined: </strong><?php echo date('F j', strtotime($pilotinfo->joindate));?></li>
will display the date as 'Month Day' like 'April 19'.