At the neighborhood pool one afternoon, I was reading and huddling in the shade, waiting for "adult swim" to start. Finally, the lifeguard blew the whistle long and loud. People started getting out of the pool, as they always do, and I got out of my deck chair and jumped in off the diving board.
When I surfaced, my friend Jill was at the side of the pool, gesturing to me to get out. I soon (but not soon enough) realized that the lifeguard had blown the whistle to get everyone OUT of the pool because of a thunderclap, which I didn't hear. He must've thought I was a recalcitrant scofflaw; jumping into the pool just as he ordered everyone to get out.