Surf Surreptitiously with Vanishd
You work hard, so you should be able to check your Facebook account or watch a few YouTube videos whenever you damn well please. But, lest the boss get the wrong idea (or lest your underlings think you're lazy), it's best to hide your extraneous surfing from wandering eyes. There are quite a few quick keys (Windows Key + D, anyone), apps, and hardware switches designed for this very common problem, but there's also a free and easy site that allows you to take care of it very easily.
First, go to Vanishd, where, after you sign up, you'll choose two layers: a staid cover site (or doc or ppt) and then the site you really want to check out (say, the Mr. Bean video below) for underneath. Your mouse will control an expandable window into the second layerit takes a little while to get used to, but pretty soon you can surf the web pretty rapidly. To get rid of the evidence? Simply right click or move your mouse off the page, and only the top level remains.