Fucks per day.
Based upon the internet meme of "Look at all the fucks I give", the abbreviation is a covert use of expressing your blissful apathy to whatever situation may arise.
Boss: 'You really need to work on improving your performance.'
Me: 'But, I have maintained a 0 fpd since 1980'
Me: 'Fucks per day ... I give 0 fucks per day'