A blank 'thank you' card sent anonymously to someone, particularly an employer or potential employer, who has treated you badly.
He opened the envelope and found a thank you card, but there was nothing written in it or on it. Completely blank. The envelope had no return address. What did this mean and who sent it to him? Was it a mistake? Hmmm?
This man received a 'thanks for nothing card' or TFN card.