Here is a way to get someone to click a Youtube embedded video thinking it's one thing, but really another. Example: They think it's a hot girl, but it's really Rick Roll.
Youtube always picks the frame in the middle of your video to be the preview frame. Insert a 1-2 second still image in the middle and it will be the preview frame. For example if your video is 60 seconds long, go to the 30 second mark and insert a still image lasting 1-2 seconds. That frame will then be the preview. Example below I made.