If you encounter message board trolls and would like to put them on ignore, here's what you do: 

Step 1.  Click the green down arrow next to the poster's name to open the poster drop-down menu.

Step 2.  Click Ignore from the drop-down menu.

NOTE: It's not a bad idea at this point to go to your My Account > settings page and check to make sure your ignore settings are the way you like them.  Remember, you can either Hide messages posted by Ignored Members, or you can gray them out ("Dim").