I was the night manager of a very trendy (and expensive) denim boutique in Ft Lauderdale for two years. The mix in the store was 75% women's/ 20% men's and 5% kid's.
I had to beg the owner to buy size 28 or 29 because she had a bad track record in selling that size to her male customers (who were affluent and larger). She (and the rest of the female staff) would always tell me to "try" the women's jeans
Just because I'm small doesn't mean I'm small everywhere. I have no ass (never did) but I've got some major legs going on and a dick that can't be stuffed casually into a 2-3" rise. The first time I tried on a pair of women's jeans I didn't want to come out of the dressing room; when I finally did there were a lot of averted eyes, and the GM called the effect "indecent".
Bigger sizes didn't work out at all, as I have no hips and no ass to hold them up, and the legs and crotch were still much too snug (and these weren't skinny jeans, either). I'm just not built like a woman or a boy, and they never looked right; I'm a real man with a man's build with a 28" waist.
Aside from fit issues, there were pockets to consider. Men carry keys, money and a cell phone. Most back pockets on women's jeans are too small for a wallet, let alone all the other junk I port around on a night out.
It was a shame, because I could have gotten some amazing deals on True Religion, Tag, Seven and AG jeans from the women's clearance table. But no deal's a good deal if the clothes don't fit, so it took almost 10 months before I had enough looks to rotate out every week without repeating.