Place bacon and vegetable oil in a large, deep pot with a tight-fitting lid over medium heat. Cook and stir bacon until crisp and brown, 8 to 10 minutes. Scatter the popcorn into the pan with the bacon and drippings and cover with the lid. When you hear kernels of popcorn begin to pop, shake the pan vigorously until popping slows to 1 or 2 pops per about 30 seconds.
Remove lid facing away from you to avoid steam and transfer bacon popcorn to a large serving bowl. Season to taste with salt if desired.