Finely dice the onion, garlic, jalapeño, cilantro, cherry tomatoes, and cucumber, then place in a stainless bowl. Tip: If you like the flavor of jalapeño but not the heat remove the seeds and ribs (the white stuff inside).
Squeeze into the diced items half of the lime then season with salt and pepper.Tip: The lime breaks the onion down so it is not so sharp.
Submerge ingredients in the tomato juice. Mix in Tajin, ketchup, hot sauce, and horseradish. Taste for heat. Adjust to your liking.
Fold in Dungeness crab then chill for at least 4 hours. Tip: If using a cooler, placing the mixture in a plastic bag would make it more practical to store.