Just look at the navbar and play with the scrollbar of the page ;) You only have to include the source javascript file and then initialize it with the following code: <script>$("div.navbar-fixed-top").autoHidingNavbar();</script>

bootstrap_autohiding_navbar.js

/*
 *  Bootstrap Auto-Hiding Navbar - v1.0.5
 *  An extension for Bootstrap's fixed navbar which hides the navbar while the page is scrolling downwards and shows it the other way. The plugin is able to show/hide the navbar programmatically as well.
 *  http://www.virtuosoft.eu/code/bootstrap-autohidingnavbar/
 *
 *  Made by István Ujj-Mészáros
 *  Under Apache License v2.0 License
 */
!function(a,b,c,d){function e(b,c){this.element=a(b),this.settings=a.extend({},w,c),this._defaults=w,this._name=m,this.init()}function f(b){v&&(b.element.addClass("navbar-hidden").animate({top:-1*parseInt(b.element.css("height"),10)+b.settings.navbarOffset},{queue:!1,duration:b.settings.animationDuration}),a(".dropdown.open .dropdown-toggle",b.element).dropdown("toggle"),v=!1,b.element.trigger("hide.autoHidingNavbar"))}function g(a){v||(a.element.removeClass("navbar-hidden").animate({top:0},{queue:!1,duration:a.settings.animationDuration}),v=!0,a.element.trigger("show.autoHidingNavbar"))}function h(a){var b=n.scrollTop(),c=b-t;if(t=b,0>c){if(v)return;(a.settings.showOnUpscroll||l>=b)&&g(a)}else if(c>0){if(!v)return void(a.settings.showOnBottom&&b+u===o.height()&&g(a));b>=l&&f(a)}}function i(a){a.settings.disableAutohide||(s=(new Date).getTime(),h(a))}function j(a){o.on("scroll."+m,function(){(new Date).getTime()-s>r?i(a):(clearTimeout(p),p=setTimeout(function(){i(a)},r))}),n.on("resize."+m,function(){clearTimeout(q),q=setTimeout(function(){u=n.height()},r)})}function k(){o.off("."+m),n.off("."+m)}var l,m="autoHidingNavbar",n=a(b),o=a(c),p=null,q=null,r=70,s=0,t=null,u=n.height(),v=!0,w={disableAutohide:!1,showOnUpscroll:!0,showOnBottom:!0,hideOffset:"auto",animationDuration:200,navbarOffset:0};e.prototype={init:function(){return this.elements={navbar:this.element},this.setDisableAutohide(this.settings.disableAutohide),this.setShowOnUpscroll(this.settings.showOnUpscroll),this.setShowOnBottom(this.settings.showOnBottom),this.setHideOffset(this.settings.hideOffset),this.setAnimationDuration(this.settings.animationDuration),l="auto"===this.settings.hideOffset?parseInt(this.element.css("height"),10):this.settings.hideOffset,j(this),this.element},setDisableAutohide:function(a){return this.settings.disableAutohide=a,this.element},setShowOnUpscroll:function(a){return this.settings.showOnUpscroll=a,this.element},setShowOnBottom:function(a){return this.settings.showOnBottom=a,this.element},setHideOffset:function(a){return this.settings.hideOffset=a,this.element},setAnimationDuration:function(a){return this.settings.animationDuration=a,this.element},show:function(){return g(this),this.element},hide:function(){return f(this),this.element},destroy:function(){return k(this),g(this),a.data(this,"plugin_"+m,null),this.element}},a.fn[m]=function(b){var c=arguments;if(b===d||"object"==typeof b)return this.each(function(){a.data(this,"plugin_"+m)||a.data(this,"plugin_"+m,new e(this,b))});if("string"==typeof b&&"_"!==b[0]&&"init"!==b){var f;return this.each(function(){var d=a.data(this,"plugin_"+m);d instanceof e&&"function"==typeof d[b]&&(f=d[b].apply(d,Array.prototype.slice.call(c,1)))}),f!==d?f:this}}}(jQuery,window,document);