Arrange the cucumber slices on a large platter in a single layer. Sprinkle with salt and pepper, cover with plastic wrap, and refrigerate for 1 hour.
Whisk the vinegar, sugar, and chile flakes in a large bowl. Discard any accumulated juices on the cucumber platter. Add the cucumbers to the vinegar mixture and toss well. Return to the platter in a single layer. Cover with plastic wrap and refrigerate for 3 to 4 hours.