I use the AdBlock+ add-on for Firefox, which seamlessly removes all ads from most websites, which is why I never see ads of any kind on YouTube.
I wanted to check a video at 50 FPS, and since Firefox does not support that yet for some reason, I watched it with Chrome. I don't have any ad-blocker there, so I get to see the ads.
Now, since YouTube is owned by Google, and all ads are provided by Google, and Google is a rather respectable company, one would think that they would only accept appropriate ads that are formal and in good taste. But what did I get? This:
Way to stay classy, Google.