IdgafISDD
Initialism for 'I don't give a fuck I'm Snoop Doggie Dog', a line from the song 'Vato', by popular rapper Snoop Dogg, used to express a complete lack of interest.
Mark: 'Guess what, my brother just won the Superbowl!'
Simon: 'IdgafISDD.'
Simon: 'IdgafISDD.'