If a player is harassing you or calling you out for no good reason, the best thing to do (by far!) is to Ignore him.
Once you add a player to your Ignored List, you will no longer see what they are typing into the chat.
To see who you have ignored, you can open the Friends menu from the icon in the bottom-left corner of the main interface.
You can also remove players from the list by clicking the “–” (minus) sign next to their name.