I want to fuck you. Rumor has it that it was first used by a famous author on the back of the envelope of a love letter to his mistress.
"IWTFY" he whispered to her.
"Not for a million bucks." she said
Acronym for "I wrote this for you" or "I write this for you"
The email message recipient was cheered up. The subject of the message was written "IWTFY" and the message body had a smiley emoticon. " :) "