If using a grapefruit, juice ½ medium ruby-red grapefruit until you have 1 ½ ounces and strain out the pulp if desired.
Fill an old-fashioned glass or copper mug about halfway full with ice.
Add 1 ½ ounces grapefruit juice and 1 ½ ounces vodka.
Stir gently to combine.
Top with 3 ounces chilled ginger beer and stir again.
Garnish with a thin grapefruit wedge if desired.
