$("p").click(function () {
$(this).toggleClass("selected", 1000);
});
<!DOCTYPE html>
<html>
<head>
<link type="text/css" href="themes/base/ui.all.css" rel="stylesheet" />
<script type="text/javascript" src="js/jquery.min.js"></script>
<script src="ui/effects.core.js"></script>
<style type="text/css">
p { cursor: pointer; font-size: 1.2em; }
.selected { color:red; }
</style>
<script type="text/javascript">
$(document).ready(function(){
$("p").click(function () {
$(this).toggleClass("selected");
});
});
</script>
</head>
<body style="font-size:62.5%;">
<p>Click me to toggle 'selected' class.</p>
<p class="selected">Click me to toggle 'selected' class.</p>
<p>Click me to toggle 'selected' class.</p>
</body>
</html>