Choose a rocks or coupe glass. Run the lime wedge around the rim of the glass to moisten. Spread the coarse sea salt or chili salt on a small plate and dip the rim into the salt so it adheres. If using chili flakes, mix them into the salt before rimming. Set the glass aside.

Make the cocktail

Add 2 oz reposado tequila, 2 oz fresh ruby red grapefruit juice, 0.5 oz fresh lime juice, 0.5 oz agave syrup, and 0.5 oz orange liqueur into a cocktail shaker.

If using, add 2 dashes grapefruit bitters to the shaker. Fill the shaker with ice (about 1 cup).

Seal and shake vigorously for 12–15 seconds, until the shaker is cold and the mixture is well-chilled and slightly frothy from the fresh juice.

If serving neat (no fizz): double-strain the cocktail into the prepared rimmed rocks or coupe glass (use a Hawthorne strainer and a fine mesh strainer to catch pulp and ice shards).

If serving as a long drink (with fizz): fill the rimmed glass with fresh ice (about 1/2 cup). Double-strain the shaken cocktail into the glass, then top with 2 oz club soda or sparkling water. Gently stir once to combine.

Garnish and finish

Garnish with a thin grapefruit wheel or a grapefruit twist. If desired, sprinkle a very light pinch of chile flakes onto the surface for a spicy aroma that pairs with the tequila and citrus.

Serve immediately. Offer a straw if served as a long drink.