In a large pot of boiling salted water, cook corn until fragrant and tender, 8 to 12 minutes. Remove ears, and hold under cold water until completely cool.
Working in a large bowl, slice kernels from cob (to yield about 2 cups). Toss with radishes, jalapeno chile, lime juice, and olive oil. Season generously with coarse salt. Serve chilled or at room temperature.
A big white daikon radish also works really well...because quite often the little radishes are wormy or don't taste the way you'd expect.