Set your oven to broil, line a sheet pan with foil, and shuck your corn. Cut the kernels onto your baking sheet, and toss with the oil. Broil the corn until there is visible charring in spots (roughly 6-8 minutes for me, but can take as little as 3-5 minutes depending on the oven. If you see or hear a few kernels jump around in the pan, the corn is done.) Remove from oven, sprinkle with the pinch of salt, and transfer to a large bowl.
In the same bowl, add the mayonnaise, roughly half the feta (reserving the rest for garnish), the chives, the cilantro, the jalapeño, and the tablespoon of fresh lime juice. Use a garlic press or microplane grater to mince the garlic straight in. Toss everything gently to combine. Taste, and add salt/pepper/lime juice accordingly.
Serve immediately, topping with the remaining crumbled feta and a sprinkling of chili powder.