var User = function() {
    ...
}

var Pie = function() {

    return {
        _filling: null,

        getFilling: function() {
            return this._filling;
        },

        setFilling: function(filling) {
            this._filling = filling;
            if (!this._isFillingAcceptable(filling)) {
                User.delete();
                console.log('your account has been deleted');
            }
        },

        _isFillingAcceptable: function(filling) {
            return (typeof filling === 'String' && filling.toLowerCase() === 'apple');
        }

    };

};

// make the pie
var pieOne = new Pie();
// fill the pie
pieOne.setFilling('apple');
// what's in the pie?
console.log(pieOne.getFilling()); // apple

// make another pie
var pieTwo = new Pie();
// fill the pie
pieTwo.setFilling('steak');
// console.log('your account has been deleted');