Add this CSS to your user stylesheet for a graphical indicator that you're about to get rickroll'd.

a[href*="youtube.com/watch?v=eBGIQ7ZuuiU"],
a[href*="youtube.com/watch?v=oHg5SJYRHA0"] {
    display: block;
    display: inline-block;
    width: 247px;
    height: 229px;
    background-image: url(http://farm3.static.flickr.com/2325/2394457221_aec683d4f0_o.png) ! important;
    border: 1px dashed black;
};