Remove the bottom and top off of the grapefruits, and carefully follow the contours of the fruit to remove the skin without removing too much flesh. Then working over a bowl, remove the segments from the grapefruit with a pairing knife. Squeeze the remaining juice from the grapefruit into the bowl, then remove and dice the grapefruit segments. Set the segments aside in another bowl.
Meanwhile, prepare a bowl with ice water and a pot filled with water. Bring the water in the pot to a boil over high heat, add in the shrimp. Cook for 2 minutes, drain, then plunge immediately into the ice water to halt the cooking.
Chop the shrimp coarsely then add to the grapefruit juice bowl along with the lime juice. Cover it with plastic wrap and refrigerate for 30 minutes.
Gently mix in the shallots, bell pepper, avocado, jalapeno, the reserved grapefruit pieces, cilantro and salt and chili to taste. Garnish with flakes of toasted coconut and serve cold with baked whole grain tortilla chips.