Edit in JSFiddle

var data = {
  labels: ['Bananas', 'Apples', 'Grapes'],
  series: [20, 15, 40]
};

var options = {
  labelInterpolationFnc: function(value) {
    return value[0]
  }
};

var responsiveOptions = [
  ['screen and (min-width: 640px)', {
    chartPadding: 30,
    labelOffset: 130,
    labelDirection: 'explode',
    labelInterpolationFnc: function(value) {
      return value;
    }
  }],
  ['screen and (min-width: 1024px)', {
    labelOffset: 80,
    chartPadding: 20
  }]
];

new Chartist.Pie('.ct-chart', data, options, responsiveOptions);
<div class="ct-chart ct-perfect-fourth"></div>
.ct-label {
  font-size: 20px;
}

External resources loaded into this fiddle: