Cause you are the mayonnaise and I am the steel

The story:

I had no idea why someone was singing about mayonnaise, and "steal" didn't fit. So my brother and I would sing it in the car "cause you are the mayonnaise and I am the peanut butter and jelly. My parents just looked at us and burst out laughing. It was many years later when I finally learned that it was magnet and steel.