Rinse squid under cold water, then pat dry between paper towels. Halve large tentacles lengthwise and cut bodies (including flaps, if attached) crosswise into 1/2-inch-wide rings.
Cook bacon in a 12-inch heavy skillet over medium heat, stirring occasionally, until golden and crisp, then transfer with a slotted spoon to paper towels to drain.
Toss squid with 1/4 teaspoon salt.
Heat fat remaining in skillet over high heat until very hot, then sauté squid with scallions and red-pepper flakes until just cooked through, about 3 minutes.
