I was born in the mid-80s so all of my associations with denim are from the 90s and aughts. In the 90s, denim where I grew up was extremely grunge influenced -- the wider and baggier the better, and the best was carpenter-style with the hammer loop etc. Anything fitted or tapered was patently uncool. By the time I got to middle school, bootcuts and flares had taken over for the girls, even full-on bellbottoms, again, the wider the better. Boy's jeans just got more and more gangsta-influenced, oversized to the max with wallet chains ubiquitous. (For men, at least, I'm sooo glad that slimmer fits have become more acceptable again!)
I don't remember what was "in" for denim while I was in college (2003-2007), I think still mostly bootcuts? And I do remember knit gauchos having a serious moment -- I jumped on board for that one. By the end of college, we were definitely in the midst of an 80s craze that brought the skinny/tapered silhouette into play for the first time in (for me) living memory. Suddenly all the hipsters were wearing thrifted mom jeans and ugly sweaters, and a couple years later the whole world was in jeggings and ugg boots!
I really appreciate that denim seems to have reached a point where there is no one "in" silhouette. Maybe it's because I'm not in high school and stuck shopping juniors departments, but it seems like there's a much wider array of silhouettes, washes, and fits available at any given time now, which I think is great.