TFD

Abbreviation for, "The fuck does."

You can use to emphasize your lack of understanding of a subject/concept.
or
Use it in a way to say that nigga's balls are cute.

HotTeacher : What is the author's intent when writing "and thou shall suck my fat fucking balls."
Student1 : TFD this even mean!? Even I don't know this useless information!
Student2 : Who TFD?