At the dawn of the industrial age trouser patterns were systematized to include a J seam. It is a pretty convenient method for manufacture, and has also clothed the bottom halves of millions since the Napoleonic wars.
Problem is of course that it’s a complete disaster! Having a flat piece of fabric from your waist to your foot only works if you don’t walk. But that’s a whole different story.
An important side effect of the J seam is that it requires a particular fit in the crotch to avoid disaster.
Too low and your bum sags, plus there’s additional stress placed on your crotch seam every time you step. Which is why a ripped crotch is your most common tear in pants.
Too high and we not only cut off circulation, but (the greater disaster) we get unsightly creases in the most inopportune places!
Hence the need to measure your inside leg when fitting pants. One could also measure from the waistband downward, but the curve of the fly would make this difficult to do accurately.
So now that you know why it’s important to get this measurement, we may as well throw in some fun history:
Legend has it that prince Albert (son of Queen Victoria I) was so conscientious about how he dressed that be pinned himself to one side of his trousers with the aid of a genital piercing. ‘Which way do you dress’ is a polite way of asking ‘on which side of your pants is your member hanging’ so that we don’t get too personal when working in that region.
Safety is also a concern, as I’m in there with some very sharp pins, and don’t much see a business pivot towards acupuncture.
So the next time your tailor asks this question, simply answer with a ‘left’ or ‘right’
Me? I dress how I vote: always to the left!!