I don't know what the F*** that means but anyway...
I think the words say it all, but basically, when there is something you completely don't understand, but don't care to take the time to understand it.
Umm, I have no idea what kind of situation i could give an example of... How's about: A nerd tells ya some stuff about computers that is too freakin' complicated for any non superbrained human to understand. So you say: Idkwtftmba!
Chick 1:"So, like I was saying, Shirley told me that Diana told her that Christi has a big crush on so and so."
Chick 2:"Really, omg, I know for a fact that he's going out with so and so."
Chick 1:"we should so totally say something."
Chick 1's Boyfriend:"IDKWTFIGO..."