Add ice to a 20oz glass. Pour in your beer. Add grapefruit simple syrup and grapefruit juice.
Stir to combine. Taste and adjust to your preference. Enjoy!
Notes
MAKE IT SWEETER: add more simple syrup and grapefruit juice.MAKE IT A MOCKTAIL: use a non-alcoholic beerGRAPEFRUIT JUICE: I prefer to buy grapefruits and squeeze the juice myself, but bottled grapefruit juice works just fine. Look for no sugar added, but if you buy one with added sugar, you will likely need less simple syrup.