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
Get the my bff jill mug.
Mom: Who are you texting three hundred times a day?
Kid: IDK My BFF Jill
by zak221133 May 9, 2007
Get the IDK My BFF Jill mug.
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
Get the idk, my bff jill mug.
1. "I don't know, my best friend forever, Jill."

2. A famously said quote on a Cingular cell phone commercial about a girl who texts alot. Her mom asks why her cell phone bill is so high, she wonders who she has been texting. The teen replys, "idk, my bff Jill?"

"Bethy!" calls mom.
(Teen girl comes to her mom)
"w.a.u?" she replys
"Your cell phone bill is whats up! All this texting!?"
"O.M.G! I.n.p.d!"
"It is a big deal! Who are you texting 50 times a day!?"
"Idk My bff Jill?"
"Tell your 'b.f.f. Jill,' that I'm taking away your phone"
(Teen hands phone to mom)
"T.i.s.n.f!"
ME PAYING THIS BILL, THAT'S WHAT'S S...N.F!"
by Quaviavid December 10, 2007
Get the idk my bff jill? mug.