Sexual harassment may include a variety of situations. It could be someone telling sexually explicit stories or jokes that make someone uncomfortable. It could be inappropriate touching.
The basic definition of harassment, according to the U.S. Equal Employment Opportunity Commission, is something that happens repeatedly. So, sexual harassment is usually an action that occurs more than once.
However, due to the incredibly sensitive and potentially dangerous nature of harassment of a sexual kind, there could be situations where one occurrence is enough. For example, if the incident is so serious that it impacts your ability to do your job or feel secure, then one time may be all it takes to make a claim.
Another example is if it impacts an employment decision, such as a manager requiring you to go on a date with him or her to get a promotion. While this may only happen one time, it is serious enough to report.
In general, though, sexual harassment requires multiple incidents where there is a resulting issue. For example, if the situation continues and leads to you feeling uncomfortable or unsafe in your workplace, then it is harassment.
General teasing or comments do not typically fall under sexual harassment. In those situations, asking the person to stop is the best course of action. You can report it as well. If it continues, then you may have a situation that allows you to make a claim.
Sexual harassment is never ok. You should always feel like you can report any incident. However, one isolated incident is usually not enough to bring a claim.