A lot of people are wondering if they can block someone on Viber. The answer is no, below is a message sent from Viber staff addressing this issue. I myself would simply tell a person that is bugging me on Viber “LEAVE ME ALONE AND GET A LIFE”.
This is an official representative of Viber Media.
Unfortunately, this feature is not available yet. We are considering to add it in future versions.
Meanwhile, we invite you to enter our Feature Request page and post your suggestion there, or join an existing similar suggestion. The more people join on a request, the faster it will become reality :)
You can find it here: http://helpme.viber.com/index.php/Knowledgebase/Article/View/43/9/have-an-idea-for-a-new-feature
For more questions or technical support, please visit our official HelpDesk or Facebook page.