The diver went below another 10 feet, but the guy joined him a minute later. The diver went below 15 more feet, and a minute later, the same guy joined him.
This confused the diver, so he took out a waterproof pad and pencil, and wrote, "Amazing! How are you able to stay this deep down without equipment?"
The guy took the pencil and pad, erased what the diver had written, and wrote, "I'm drowning, you moron!"