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'
Frozen penis disorder. Occurs when running outside on a very cold day, ones penis get extremely cold and changes colors. Victims of this disorder experience extreme pain when defrosting their manhood in the shower.
I was running outside in the snow yesterday and got FPD! My dick turned white!
Scientific notation for "Faps per day"
This new fetish of mine has increased my fpd to 5!