What term describes the act of annoying, bothering, or harassing someone?

The term that accurately describes the act of annoying, bothering, or harassing someone is "vex." When someone is vexed, they experience feelings of irritation or frustration due to the actions or behavior of another person, which aligns with the definition of the question.

The other terms do not convey the same meaning: "viable" refers to something that is capable of working successfully or living; "vilify" means to speak or write about in an abusively disparaging manner; and "vivacious" describes someone who is lively and animated. Thus, "vex" is the term that best fits the description of causing annoyance or harassment.