hideignore.user.js

// ==UserScript==
// @name                Hide Ignored
// @namespace           sechatign
// @description         Hides the small squares of users in StackExchange chat sites.
// @include             http://chat.stackoverflow.com/*
// @include             http://chat.stackexchange.com/*
// @version             1.0
// ==/UserScript==

function hide() {
    var ig = document.getElementsByClassName("ignored");
    for (var i = 0; i != ig.length; ++i) {
        ig[i].style.display = "none";
    }
    window.setTimeout(hide, 100);
};
hide();