Woke up this morning thinking of the phrase "Don't get your panties in a bunch". This of course is the Americanized version of "Don't get your knickers in a twist" or "Don't get your knickers in a knot". The point of all of the phrases is basically to tell someone to "relax!" or "don't worry so much about this".
I have two main issues with this phrase. First underwear today has so little material that it would be difficult to get it in a bunch, twist or knot. For example - how would one knot a thong? Secondly panties are normally associated with women giving the phrase an overtly sexist tone.
My suggestion? Replace the phrase "Don't get your panties in a bunch" with the phrase "Release your wedgie!" Everyone knows how uncomfortable wedgies are and both men and women get them. Language issue solved.
Now I may go back to bed.