Add the lemon base: Pour the lemonade, pineapple juice, and fresh lemon juice into the Ninja SLUSHi vessel through the easy-fill port.
Start the slush cycle: Close the cover, press the power button, and select the Slush setting. Let the machine run for about 20 minutes.
Add the vodka: Once the mixture starts to thicken, open the cover and pour in the vodka. Switch the machine to the Spiked Slush setting.
Freeze until ready: Continue running the machine for about 40 minutes, or until the Lemon Drop Slush reaches a thick, spoonable texture. Use the machine's ready indicator as a guide.
Rim and serve: Dip the glass rim in water or lemon juice, then coat it with sugar. Place the glass under the dispenser, slowly pull the handle to fill it, and garnish with a lemon wheel or twist.