Similar to BFF but without the girly connotation. What you'd call your best buddy who you know will stick with you through thick and thin. You look forward to hanging out and doing shit with them and there's always better things to come. Even when they've gone someplace far away it still feels like they're there with you. They're not just your best friend, they're your fuckin' best friend.
MY: See ya later, my FBF
The FBF is a well know "meme" on 4chans /b/ random board, it is a picture of a bullfrogs head with a green pattern background, people add text on a website called meme generator that is agreeable and adheres to "foul bachelor behavior". This is one of the most popular memes on the /b/ board as many people who frequent /b/ can relate to it.
The text that people put on the picture is usually in a simple "event" - "reaction" context (see examples)
The text, when done properly usually contains a common, normally undesirable character trait being expressed, such as wearing dirty clothing, "fapping" (masturbating) into a sock, wearing a fapped into sock, microwaving a harddrive out of paranoia, not caring about surroundings, being disoriented about what time it is after an unexpected nap, etc. etc.
(Bottom) Fap 2 minutes later
(Top) Clothing worn once on the floor
(Top) Wake up, see 2:00 on the clock
(Bottom) Look out window to see if AM or PM
You get the gist of it. FBF.
1) The facebook version of a "BFF.";
2) A person that you are friendly with and/or think is cool but don't necessarily hang out or know.
b. New acquaintance: "Hey, it was really good meeting/you hanging out last night. Let's be FBFs and get together soon."
c. You: "I wouldn't say were like friend-friends...we're just FBFs."