Annoying kid...

There's this kid in my gym class, who was also in my class last year. He always tries to talk to me, and flirts with me, and he's being really mean and creepy. I'm not interested in romance, and I want him to know that. He's very self-centered, and a real jerk. I tried telling him to stop, but he won't. I tried to tell an adult, but that didn't work out either. At the moment, I'm ignoring him, and hoping for a miracle. Does anyone have any suggestions on what I should do?