If there are particular members that are bothering you and you do not wish to see their posts or receive Private Messages from them, then you can add these members to your 'Ignore List'.
In the top right of the forum, click your Username. A dropdown menu will appear and from here you need to select 'User Settings'. On the page that appears, click 'Account' and scroll to the bottom. In the text area next to 'Ignore List', enter the Usernames of users that you want to Ignore.