It means you are down for the fuck and anyone can be down for the fuck; you, your mom, your dad, your sister, your brother, your uncle, your teacher, your aunt, and of course your friends.
Don't Fear The Foam. Used in the homebrew community referring to the foam made from using StarSan, which many people take unnecessary actions to get all of it out of their vessels, sometimes introducing more contaminants into their brew in the process.
Gene: "We have to shake all this foam out of the bottles before we can rack them!"
Richard: "DFTF, bro. We're good."
Drinking From The Fire Hose
TLA for any situation where a very large flow of information is coming your way, and you have to retain some part while simultaneously keeping from being overwhelmed.