Cool Kid Syndrome!

coolguysyndrome.user.js

// ==UserScript==
// @name         Cool guy syndrome
// @namespace    http://vresod.github.io
// @version      1.0
// @description  cool kid sydrome
// @include      *
// @author       Vresod
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    var chance = /*1 in*/ 10;
    var x = Math.floor(Math.random() * (chance - 1)); // returns a random integer from 0 to chance
    if (x == 0){
        alert('you are a cool kid!')
    }
})();