No doubt about it, french cuff shirts are fancy, and jeans are not. That doesnt mean you cant wear them together. I find that the most stylish men I know are masters are putting together completely disparate elements, yet somehow pulling it off. The world would be a boring place if everyone went around saying "cant do this, cant do that", because of the formality of certain elements of clothing. I love wearing a really well made cashmere v neck sweater (fancy), with a old frayed BB oxford underneath (not fancy), with a great old pair of levi 501s (not fancy), with a pair of english made suede chukka boots (fancy). Im not trying to say im some fashion plate or anything like that, but mixing and matching looks great to me. maybe im in the minority, i dont know. getting back to the topic at hand, I often wear the aforementioned levis with a T&A french cuff shirt, and a suit jacket taken from one of me suits. I wouldnt wear a pair of tiffany sterling knots for the links with this outfit, but a pair of silk knots, or something like it, work just fine.