Prepare a grill for medium-high heat. Brush ears of corn with butter; season with salt and pepper. Grill, turning occasionally, until kernels are very tender and charred in spots, 10–12 minutes. Let cool slightly, then cut kernels from cobs.
Whisk lime juice, honey, Sriracha, granulated garlic, and 1-1/2 teaspoon salt in a large bowl to combine. Add corn, avocados, chile, cilantro and radish to vinaigrette and toss to combine; season with Old Bay Seasoning. Cover with plastic wrap, pressing in direct contact with salad to prevent avocados from turning brown. Chill at least two hours.