Stop responding. Don't wave back, don't speak, just walk on by. If the person insists on getting in your face and making conversation, tell him clearly that you do not want him to bother you anymore. Don't make explanations, just say you don't want him to bother you, and you want him to leave you alone. If he bothers you again, call the police and take out a restraining order against him. If you have a smartphone, record yourself telling him that you don't want him to bother you again.