One who adds you as a friend on Facebook, but is not really your companion. This person does not require to be an enemy. An unknown stranger, or someone you have never met who adds you can also fall under this category.
+ You have a friend request.
*Facebook Foe's Name Here*
You have X friends in common.
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*Thought in head (or possibly even aloud)* - "Who does this Facebook foe fuckface think he is?"
a facebook friend who is also in your circle of actual friends, but who never checks his facebook.
"Hey is Johnny coming tonight"
"I doubt it. I put a post on his wall a couple of days ago but he never checks it. His my biggest facebook foe."