You have your choice of News Readers to read RAS and some of them allow you to
filter individual posters. RAS is fundamentally just data. A News Reader is a tool to display and interact with that data.

http://en.wikipedia.org/wiki/Newsreader_%28Usenet%29

Google Groups (a News Reader for RAS) allows you to report topics as "abuse" for the "other" reason and this hides the topic, but only for you. Once a number of people report the thread as "abuse" it is flagged for other users (but only in some news readers.) You have to pay for the corporate version of Google Groups to obtain the functionality of filtering individual posters (so a free news reader is a good option).

Poke around in the options for your News Reader and you may find what you're looking for. It's worth the effort to learn how if you spend any time at all on RAS.

Use Google to search for "News Reader" to find out more. There are lots of articles that review the various tools (aka News Readers).