Make lemon syrup by combining hot water, sugar and lemon juice.
When syrup is cool, make drink by combining 3/4 ounce of lemon syrup with citrus vodka, lemoncello, lemonade and ice in a blender. Blend on high speed until ice is crushed. Start with one cup of ice and add additional ice, if needed, to make drink slushy. Serve in a 16-ounce glass with a straw and a thin slice of lemon on the rim of the glass.