Tf

Tf has two main uses.

tf, the most common one, is an abbreviated version of "the fuck?", usually as a shorter substitute for wtf, "WHAT the fuck?". Usually used in circumstances of confusion or indignation.

TF, the less common one, stands for Transformation Fantasy. This is a fetish for people who find sexual attraction to the idea of transformation, whether physical, mental, spiritual, or any combination of the three.

1.
John: Ayo, I found this weird video!
Zach: tf? That's NASTY, get help.
2.
Michael: Hey, Wanna engage in some TF?
Samantha: Who tf are you?