ICTYBTIHTKY

ICTYBTIHTKY

humorous An initialism for "I could tell you, but then I'd have to kill you," meaning, if I told you this extremely confidential or sensitive piece of information, I'd have to kill you to ensure that you don't share it with anyone else. All she wrote back was ICTYBTIHTKY, so I guess I'll never know the big secret.
Farlex Dictionary of Idioms.

I could tell you but then I’d have to kill you

and ICTYBTIHTKY
sent. & comp. abb. a phrase said in answer to a question that one does not want to answer. Don’t ask. ICTYBTIHTKY.
See also: but, could, have, kill, tell

ICTYBTIHTKY

verb
See I could tell you but then I’d have to kill you
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • FTFY
  • WTG
  • DYOR
  • GMTA
  • YKWIM
  • CBA
  • DAF
  • CTFO
  • DBEYR
  • CYA