When you send a YouTube video to a friend, they'll usually have some context about the video before they even watch it. At the very least, they'll see a title, some ads, or a view count. If you want to catch them unawares, Suprise.ly strips all that away and lets you share just the video.
All you need to do is drop a YouTube link into Suprise.ly and it will generate a link to a clutter-free version of the video. You can also create custom starts and stops or link to a video with different audio if you like. Your recipient gets a link that opens the video full-screen without all the junk. Yes, it could be used for some advanced Rickrolling, but it's also just a cleaner way to watch videos.