Top Definition
Best sister/friends
When two best friends are so close that they consider themselves as sisters !
- Pauline and Catherine are really close!
- Yeah! They're BSF s :)
by foreveryounnng May 12, 2012
"Bull Shit Foursome"
Four friends who often go out together on random crazy adventures and day trips.
Let's go out BSFing this weekend!
by Cindy5 January 24, 2009
Someone who is a BOOB STARING FREAK. Usually straight guys.
"oh my gosh that chick has got a nice rack!"
by CoolerThanYou32197392183 January 23, 2009
"Bisexual Foursome"
Four friends who often go out together on random day trips together.
Hey, you guys want to come out on a BSF day out soon?
by loz333 March 20, 2008
BSF - Best Skype Friend

When you have a best friend, who is on skype.

This could change if you have a better friend on Facebook or MSN

BSF is only related to Skype
Ryan is my BSF. I enjoy sending him poems.

Ben is not a good BSF he talks to other people on skype more than me.

Ben - Hey will you be my BSF?

Travis - No how could you say that? I already have one!
by TheRealWord January 13, 2011
Best slutty friend- The friend of an ex-slut has from her 'wild years', who unashamedly knows all of her dirty secrets, and more often than not was present for some of them.

The BSF will of course have shared at least one, if not two (and sometimes at the same time) boyfriends or lovers of the subject.

Whilst the subject does her best to hide her past the BSF loves nothing better than to loudly discuss her current and future sexual conquests in front of anyone who will hear.

The BSF of course must naturally do her best to either break her friends relationship so she can bring her back into the slutty fold, or be apathetic about a break up and never encourager her friend to actually try and make something of her life.
Sally and Angie had been friends for years, So sally invited Angie to her wedding. Angie then screwed sallys husband and two of the grooms that night, Angie asked why she did it, she said I am your BSF!
by captianstabber May 17, 2014
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