Foe allows you to make any existing friend into a Foe.
A foe will have a skull pawn on the user list and in the chat box, meaning that they are your enemy. Unlike a friend, a foe will not be able to override your NOPM/NOPC powers. They will also see not added you as a friend when they click on your name.
To make someone a foe, you must have them added first. Open your friends list, click on the user you want to make into a foe, and click Foe. To return a foe back into a regular friend, click on their name again and click on Un-Foe.
Note: Moderators and above will always be able to private chat/private message you.