Add sour cream, mayonnaise, salt, pepper, and vinegar to make dressing. Make in separate small mixing bowl and whip together with fork.

Stir in 2/3 of dressing into peas until they are coated. Stir in bacon, cheese, most of parsley (if fresh; if dry add all), and onion. Taste and adjust seasonings; can add more salt and pepper if needed.

Chill for 2-4 hours. Mix in extra dressing and top off with fresh parsley.