From the Menu--Triggerman--Sanctioned--Barzini Hit (20 minutes)--Easy--
As soon as it starts, go to the map, hit 3 times, and go down to Barzini's 'Palermo Warehouse'. Mark it with the red flag indicator. Go to it and take out all of the Barzinis on both sides guarding the warehouse. Since the entire place has Barzinis businesses around it, a bunch of Barzinis will come and attack you, which makes this even easier. Once you take out all of them you should have between 10-15 kills. You should then go to the warehouse and kill as many people as you can. Once you die you'll be taken to a hospital about 10 seconds away. Rinse and repeat.