I don't like the cut of your jib

A ship's jib is a triangular sail set at the front of the vessel, and its particular shape, its "cut," varied noticeably between different nations' shipbuilders. Experienced sailors could identify a ship's origin, and guess whether it was friendly or hostile, just by studying the cut of its jib from a distance, long before the vessel was close enough to show its flag. Lord Byron used the phrase figuratively in print in the 1820s, and it stuck.