In reference to Best friend forever, as in the commercial...
Mom: Who are you texting so much?
Girl: I DK, my BFF Jill

Anyone you hang around a lot, for work related reasons or otherwise, even if they aren't your best friend.
RIck: AnnMarie, where is your BFF Jill?
AnnMarie: I don't know. I feel lost without her, we've got to get this project done for Monday.
by Lanny123 June 16, 2007
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1- A person you consider your friend, but not your most favorite person.

2- secondary bestfriend.
"I was at the mall the other day and saw my bff jill. i was dreding every second of that hideous conversation."
by Kay Luh September 11, 2007
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hold out your right hand in front of your face, fingers spread out, palm away - the fingers of your hand should spell out "jill" respectively; referred to when someone is suspected of masturbating
you were in your room for awhile. spending quality time with your bff jill?
by dulcedelecheistheshiit December 17, 2008
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from the cingular texting commercial

mom: " you have you been texting 50 times a day?!"
stephanie: "idk, my bff jill?"
by clairerocks June 13, 2007
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Means "I don't know". A shortened form of "IDK, my BFF Jill?" from the Cingular commercial.

Mom: "Beth Ann!"
Beth Ann: "WU?" (What's up?)
Mom: "Your cell phone bill is what's up. All this texting!"
Beth Ann: "OMG, INBD!" (Oh my God, it's no big deal!)
Mom: "It is a big deal. Who are you texting 50 times a day?"
Beth Ann: "IDK, my BFF Jill?" (I don't know, my best friend forever Jill?"
Mom: "Tell your BFF Jill that I'm taking away your phone."
Beth Ann: "TISNF!" (That is so not fair!)
Mom: "Me paying this bill, that's what's...S...N...F!"
Person 1: Dude, where'd you get those jeans?
Person 2: Uh, my BFF Jill.
by Elvi December 31, 2008
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Mom: Who are you texting three hundred times a day?
Kid: IDK My BFF Jill
by zak221133 May 9, 2007
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A funny quote from a cell phone service provider commercial (that probably doesn't work, but their advertisers know how to do a good job) after a mother asking their young daughter why the texting bill is so expensive. It's a common way to answer annoying questions to Myspace surveys or generally obnoxious questions
Annoying girl says, "So, who do you have a crush on?"
Response, "Idk, my bff jill."
by Basket Case October 16, 2007
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