My first aikido instructor taught me from day 1 to "glue your hand to your forehead" - which a perceptive friend of mine immediately likened to the picture on the cover of the Greatful Dead's Live in Europe 1972 (the guy with the ice cream cone splatted to his forehead).
I used to visit a dojo in London where the teacher used to use exactly the same phrase, he referred to the exercise as 'sheer agony' just to further get the point across. It definitely gets you to focus on keeping your hands on your own centre line, which is where most people go wrong with shihonage.
Personally if I didn't have metaphors to use to help me to teach aikido I'm not sure quite how I would get many points across.
I have some really bizarre favourites, which I hesitate to even mention here, because without the benefit of me visually demonstrating what I am talking about, they would just sound daft
We need metaphors to make sense of things which are difficult to grasp.