Melt the coconut oil in a large skillet over medium heat. Add 2 kernels of popcorn. Once they pop, add the rest of the kernels, shake the pan lightly to distribute the oil. Cover the pan with a lid, but tilt or crack it slightly to let steam escape.
Meanwhile, in a small saucepan over medium-low heat, melt the butter. Add the brown sugar, curry powder, cayenne, and salt; whisk vigorously to combine. Keep warm while the popcorn pops.
When the popcorn finishes popping, immediately pour the warm curry butter over the popcorn while it's still hot. Stir thoroughly. Transfer the popcorn to a large bowl and shake to make the unpopped kernels settle to the bottom.