Copy and paste the code below into the head of your formname.html directly below this line.

<!-- End of the headers for CoffeeCup Web Form Builder -->

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.6/jquery-ui.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function () {
var holidays = ["02-14-2015","02-16-2015","03-16-2015"]; //Enter the needed dates here.
$( "#item1_date" ).datepicker({
beforeShowDay: function(date){
var datestring = $.datepicker.formatDate('mm-dd-yy', date);
return [ holidays.indexOf(datestring) == -1 ]
}
});
});
</script>

Change the date pickers id in the formname.html to what I have mine set to in the script.

item1_date