Ingredients
Method
Stir together 2 Tbsp. Diamond Crystal or 1 Tbsp. plus ½ tsp. Morton kosher salt and ½ tsp. Aleppo-style or other mild red pepper flakes on a small plate. Moisten half of rim of 6 rocks glasses with ½ lemon, then press into chile salt to coat. Set aside.
Purée 4 lb. seedless watermelon, rind removed, flesh cut into large cubes (about 5 cups), in a blender until smooth. Strain through a fine-mesh sieve into a pitcher, pressing on solids; discard solids. (You should have 3–3½ cups juice.) Add 1 cup gin, ½ cup fresh lemon juice, and 3 Tbsp. Campari to pitcher; stir well to combine.
Fill prepared glasses with ice; divide punch among glasses.