Worst Friend Forever. Your WFF is that friend that you laugh and joke a lot with all the time, but you are always fake being mean to him/her and don't give him/her some of your cookie on your birthday. Usually used between people of the opposite gender. When you tell someone that you consider them your WFF, they will know that you do not like them at all but they are still considered the awesomest friend ever. They will also know that all your teasing means absolutely nothing.
Lily: So I heard that Nick's your best guy friend, but you are always so awful to him!
You: Naw, we're WFF's.
Lily: Oh I see so you won't be mad if I ask him out?
You: He's all yours.