It means Best Friends Sister. Commonly used when one is in love with best friend sister.
"Bro I like your sister."
"So you're in love with your BFS?!?"
"Yes, yes I am."
There are three logical meanings
1. Bowling For Soup (one of the best bands ever, they sing 1985).
2. Bull-fucking-shit
3. Boyfriends, since bf is boyfriend (apparently)
"Hey did you see that new Bfs video?"
"What there's a new one!?"
"I mean I'd never do that!"
"Bfs, dude."
"I was txtng my bfs n accdntly mixd there namez!"
Bearded Fuck Stick (noun) a man, typically a man who works for the city, who has a beard to rival Gandalf and is dirtier than a sewer rat.
scott: was that a yeti?
Bill: No, That's just a BFS.