Quid Pro Quo
The other form of sexual harassment is Quid Pro Quo which is Latin for "this for that" or "something for something." Quid pro quo harassment occurs when employment decisions and conditions are based upon whether an employee is willing to grant sexual favors.
Quid Pro Quo is based in power and control and so not often seen between co-workers, but between employees and supervisors.
If the employer denies the employee a "tangible job benefit" such as a promotion or a pay raise, or alternatively fires or avoids hiring someone because of sex, that could be considered quid pro quo harassment.
A person does not have to prove that they suffered economic loss (e.g., been denied a promotion or raise) to prove quid pro quo harassment. It is enough to show a threat was made or implied.