These all happened awhile ago, but they were all at Lincoln Park Zoo and on different occasions.
The first one was in the primate house. This woman was with two kids standing at the red-ruffed lemur exhibit. The woman tells the kids, "These are lem-yours. Do you see the lem-yours?" I subtly tried to correct her by saying aloud, "Wow, the lemurs look really cool today," but she didn't hear me/didn't care. Not a huge deal, and more amusing than annoying, but still notable.
Another time I was standing at the red panda exhibit, and I was actually recording a video of them. This woman behind me - who I don't think knew I was recording - says in a high, annoying voice, "What does the red panda say?" and then cracked up laughing. This was right after that song "What Does the Fox Say?" came out and I think she was trying to be funny. It wasn't.
The worst, though, was back in 2018 when I brought a friend of mine from out-of-state to the zoo. We were in the Small Mammal/Reptile House, which contains a small, dark cave where the fruit bats reside. The bats are behind glass and can't get to you, but these children on a field trip were all screaming bloody murder because they were afraid of the bats. I actually heard someone - don't know if it was a zoo staff member or a chaperone - telling the kids to be quiet, but they weren't doing so. That building is also a bit of an echo chamber, so you could hear the screaming throughout the main gallery.
In general, I also hate it when people point out when an animal relieves itself or starts mating. I remember at the zoo in Des Moines, the male ostrich relieved itself in front of a large crowd and everybody was all, "Ewwww!" and groaning.