We've all seen people who do this

jQuery('a').each(function(){
    jQuery(this)[0].innerHTML += ' proccessed';
});

function letsPoluteNS() {
    polute = '';
    for (morePolution = 0; morePolution < arguments.length; morePolution++)
        polute.join(arguments[morePolution]);
    return polute;
}

and so on. I was wondering what people have seen the most common javascript/jQuery technique that is slowing down the page and/or wasting time for the javascript engine.

PS I know that this question may not seem to fit into whats an accepted question, yet I'm asking for what the most common accepted waste is