Place the watermelon cubes into the blender and blend on high until completely pureed and smooth, about 30 seconds. Check that the mixture is liquid and uniformly pink, with no chunks remaining.
Pour the watermelon puree through a fine strainer into a pitcher to remove excess pulp for a smoother drink. Press gently with a spatula to extract as much juice as possible, then discard solids.
Add lime juice, tequila, and honey (if using) to the strained watermelon juice. Stir well to combine, resulting in a vibrant, uniformly colored liquid with a sweet and tangy aroma.
Prepare the glass rims by placing salt on a small plate. Moisten the rim of each glass with a lime wedge, then dip the rims into the salt to coat evenly.
Fill a cocktail shaker with ice cubes, pour in the watermelon mixture, and shake vigorously for about 15 seconds until well chilled and slightly frothy. Listen for a clear shaking sound and see the mixture become cold and slightly diluted.
Strain the shaken cocktail into the prepared glasses, pouring over fresh ice if desired. Serve immediately with a slice of lime or watermelon wedge for garnish.
