OK, I have 2 instances I can think of off the bat so here goes...
the bigger more overarching instance of sexism I saw was in my workplace--my first job ever, actually. I was 16 working at a local hardware store. They forced me to be on register duty even though I was perfectly capable of working the floor, simply because "the girls were the cashiers, and the guys were the sales associates". Okay, cool, except I would rather be an associate because it pays more, while at the time the cashiers literally made federal minimum wage, no more. I worked there 2 years and never got a damn raise even though my work was as good as the guys'. I digress. It gets more heinous because APPARENTLY a guy who worked at this store long ago once stole from the register, and ever since, guys weren't really allowed on registers, which is totally stupid for a number of reasons. I don't know, my boss was very....traditional, I suppose you could say. Very set in his ways that girls did one thing, guys another, no exceptions. The same man, incidentally, who got mad at me for saying "Happy Holidays" to people instead of "Merry Christmas"...
I was so happy on the day that I quit, no 2-week notice ;)
Second thing that has always irked me is how people assume if you're a girl or woman, you automatically want marriage and kids. Now that I'm older, this is something I definitely want in the future, but that's not the case for everyone. I think specifically about my neighbors, who are actually very nice people, but one of the first things they said to me upon moving in next door was "omg you can babysit!" and I was like....um, no. Thanks for assuming when I don't even want my own children yet, let alone the responsibility of watching someone else's. I was told I was overreacting for getting annoyed by that because "they pay so well!" but that doesn't really matter to me. My boyfriend (same age as me, and even gets along with kids better than me) was right next to me and the neighbor literally addressed me specifically and not him, almost as if because I'm a girl, I MUST be the one who will be a caretaker. I know it's petty but to this day I give them the cold shoulder because I don't want them assuming a thing about me when they don't know me at all. I'm only gonna say this once: F*ck. Them. Kids.
Anyone else deal with comments and assumptions like that from older people specifically, assuming that a girl or woman will take on the "traditional" mom role? It aggravates me that even in 2019, a lot of people still see women as incubators only (don't get me going on the United States abortion laws right now!).
I can only imagine how it would feel for, say, someone who doesn't want kids or can't have them. It's not that deep, but at the same time, it does carry implications that are still inherently sexist even if it's not a conscious thing for most of us.