it sort of makes a bit of sense and went something like this:

"It is an expression coming from Great Britain. The origin of the saying reflects an upset, agitated person angrily screwing up their clothes (underwear/knickers makes it sound funnier I guess lol) and throwing them in the dresser drawers as opposed to carefully folding them up."

I think it just went on from there and became anything from “don’t get your knickers in a knot” to “don’t get your underwear in a bunch” and the US version: "don't get your panties in a bunch" etc.