In a large skillet over medium heat, cook bacon until crispy, 5 to 8 minutes. With a slotted spoon, remove bacon, leaving fat in skillet; drain on a paper towel. Set aside.
Increase heat to high; fill skillet with as much spinach as will fit. Season with salt and pepper. Cook, tossing spinach and adding more as it wilts (it may take up to 2 minutes to fit it all). Continue to cook until tender, 1 to 3 minutes.
Tilt skillet to drain water from spinach (using slotted spoon or a spatula to hold spinach back). Mix in vinegar; season with salt and pepper. Serve sprinkled with crispy bacon.