Put the ice cubes in a mixing glass. Add the gin, vodka, rum, tequila, Cointreau, lemon juice and sugar syrup. Stir well, then strain into a tall glass filled with ice cubes. Add enough Coca Cola to fill the glass, and decorate with the slice of lemon.
To make sugar syrup, heat 1 cup sugar and 1 cup water in a small saucepan until the sugar dissolves.