Harassment can include, for example, offensive or derogatory remarks about a person’s age. Although the law doesn’t prohibit simple teasing, offhand comments, or isolated incidents that aren’t very serious, harassment is illegal when it is so frequent or severe that it creates a hostile or offensive work environment or when it results in an adverse employment decision (such as the victim being fired or demoted). The harasser can be the victim’s supervisor, a supervisor in another area, a co-worker, or someone who is not an employee of the employer, such as a client or customer.