In a small bowl, mix the sour cream, mayonnaise, salt, pepper, and vinegar together to make the dressing.
Stir two-thirds of the dressing into the peas until the peas are coated. Gently stir in the bacon, onion, cheese, and parsley until all combined. Taste and adjust the seasonings. Cover with plastic wrap and refrigerate 2 to 4 hours before serving. (Pop the extra dressing in the fridge, too.)
Remove from the fridge and stir in the rest of the dressing to your liking. Sprinkle with more parsley before serving.
