Literal translation
straight as my arm when I blow my nose
Meaning
not straight in the least
Explanation
Not straight at all, literally or figuratively, said of a badly drawn line or an unscrupulous person. The image, ironic by antiphrasis, a common device in Provence, takes as its reference the arm at the moment of blowing one's nose, an unseemly gesture that reinforces the negative connotation. One also says dre coumo la gambo d'un chin, like a dog's leg.