You have several options for privacy to choose from on the chat gump, use the [c command in-game

Select your Status:

Online - Shows other players you are online
Away - Shows that you are away from your keyboard
Busy - Busy means you are not wanting other players to interrupt you
Hidden - Hidden means other players cannot see your online status and you do not want to be contacted

If a player is bothering you or you do not wish to have any contact with them type [c in game to open the menu, select the "Q" menu. Now you can add them to your chat ignore list by selecting "i" next to their name on the player chat list. If it turns green, you are ignoring them.

You can also select "hidden" on the status selection and the offending player will not see you online or be able to contact you.

Many players enjoy this option because it's "old school" or "roleplay" style and disable chat so that the only contact they have is the text chat in-game when they actually encounter another player