We've heard of many add-ons for guac, but grapefruit and tequila? Count us in!
Halve the grapefruit through the stem end. Cut the peel and white pith from 1 half. Cut between the membranes to release the segments onto a cutting board and chop. Juice the remaining grapefruit half.
Scoop the avocados from the skins into a medium bowl and mash with a fork. Gently stir in most of the chopped grapefruit (reserve some for garnish), 1/4 cup of the grapefruit juice, 1/4 cup onion, the chopped cilantro and jalapeño, the tequila, 1/4 tsp. cumin, and a generous pinch of salt. Top with more onion, the reserved grapefruit, the remaining 1/4 tsp. cumin, and the cilantro leaves. Serve with tortilla chips.