A common Australian Colloquialism (or is it British) is 'Don't get your knickers in a knot'
But what does it mean? The freedictionary.com says this: to become very upset about something, usually something that is not important. Example:
'Now, before you get your knickers in a twist, let me explain the situation.'
There are seemingly many variations of this phrase, such as “don’t get your knickers in a knot” and “don’t get your underwear in a bunch”. One might wonder, who in the world came up with this? After all, how would one get one’s underwear twisted in the first place — putting them on too fast? the washing machine did it? And is one walking around all uncomfortable with a wedgie, or is one simply having a difficult time putting on his or her underwear?
Anyway this from Not One-Off Britishisms...
Here’s the deal. Knickers in a twist is indeed a Britishism, derived from the British sense of knickers as (in the Oxford English Dictionary’s definition)
“A short-legged (orig. knee-length), freq. loose-fitting, pair of pants worn by women and children as an undergarment. In extended use, the shorts worn by boxers, footballers, etc.”
The twisty figure of speech first appeared in the U.K. in 1967, according to Google’s Ngram viewer, quickly gained popularity through the mid-1980s, and has leveled off since then. In the U.S., by contrast, the phrase’s popularity grew quite gradually through the early ’90s, when it took off; it’s now used more here than here.
The Cambridge International Dictionary of Idioms (published in 1998) says that "get your knickers in a knot" is "Australian, informal," and that "get your knickers in a twist" is "British & Australian, informal"—but it doesn't say when either expression came into use.
And then there's the American "don't get your panties in a bunch"
OK, so who's saying is it? If you can shed more light on the saying then please comment.
If'n you do get your knickers in a not however, you may end up sounding like this...