Treacherous Swine is your first mission for Colonel Cortez. The Colonel asks you to take out the loose-tongued Gonzalez with a chainsaw no less.
To complete the mission head over to the area indicated on the map and park a vehicle outside ready to jump into later in the mission.
After the cut scene you can either use the chainsaw or switch to another weapon to take out his two henchmen. Gonzalez will make a run for it at which point there will be a second cut scene outside the building.
Switch to select a gun and take Gonzalez out at which point you’ll pick up two stars. To the left of the building’s exit is a star which will lose you a wanted star. Then jump into your vehicle and just by driving away you’ll lose the other star soon enough and earn $250. Alternatively, head over to the Pay’N’Spray as indicated in the main picture to lose any remaining stars.