It means Chill The F*** Down, or Calm The F*** Down,
usually used when one person gets mad at
something simple, which wasn't meant to insult. Also used to calm
someone down before a Beef.
#1 "Dude, Stace went to
the Movies with Robert"
#2 "WHAT?!?!?!?"
#1 "Dude, CTFD she went with her Posse"
"Yo mamma so stupid she put paper on the
television and
called it paper view!"
"What you say 'bout my mamma?!?!"
"CTFD, It was a harmless joke"