Greg Who Cooks
Executive Chef
I learned "knickers in a twist" from my Scottish ex, way before I ever heard "panties in a bunch". Until I moved to Denmark and had English friends, I thought knickers were trousers tha end and are tight just below the knee.
Google define:knickers and you'll get both the loose fitting trousers gathered at the knee/calf and woman's/girl's underpants. If I remember my women's panty history in past eras women wore longer underpanties, not the bikini that (as far as I've seen) are popular with present day women.
Thus the expressions are IMO equivalent.