Something that's eye-popping is shocking. If you pull off an eye-popping reverse 2 1/2 somersault dive at your local pool, you will probably make quite a splash. (Get it?)
An eye-popping profit from your lemonade stand might be a remarkable pile of quarters. The eye-popping dress you wear to a formal party makes such a strong impression on the other guests that many of them say, "Wow!" when they see you. This informal adjective comes from the cartoonish idea that someone could be so impressed or amazed that their eyes would pop out of their heads.