Thoroughly wash your grapefruit.
Using a vegetable peeler, remove the rind from the grapefruit. Try not to get the white pith underneath the rind. Set aside.
Place grapefruit peels in a pint mason jar.
Add tequila and place the lid on the jar.
Set the jar in a cool, dry place out of direct sunlight.
Let sit for at least 24 hours.
Note: Be sure to pay attention to timing here. Leave it for multiple days and you will start getting a bitter taste in the infusion.
Remove the grapefruit peels from the tequila. You can leave the tequila in the mason jar or decant it into a prettier container.