One non-tobacco-related confirmation bias I've noticed, which has irked me to no end lately, is that people have now decided that men's suits should fit a man like yoga pants, and view this as a good and flattering fit!
(Mostly younger) men are wearing suits, sport coats, and trousers so short and tight that they literally look like Peewee Herman. Notably, Peewee Herman's suit was intended to be comically ill-fitting and small, like a child growing out of a too-small suit, yet Peewee's suit is actually baggier than some of the more daring on-trend cuts today. The reason this irritates me is because so many manufacturers are catering to this trend that it is getting increasingly difficult to find suits / business attire that fits in a manner appropriate for the professional world, without being super baggy and shapeless. Even finding a good pair of khakis these days that are 100% cotton, with no spandex, is getting harder. If you don't like the cut from the handful of manufacturers that still make them in 100% cotton, then you're out of luck.
EDIT: I realize the above suit cut preferance might not necessarily be a confirmation bias. My thought is that people are getting this idea that because a few skinny models look good in these slim cuts, and that the skinny suit look is all over the place in advertising, then they themselves should also wear, and will look good in, a skinny suit, when in fact, a slightly more traditional cut, I believe, is objectively more flattering to the average male physique.