My peeve would also be getting the breed wrong. Especially when it is totally obviously not the breed they think it is.
There was a guy at the dog park once that in the point of me and another gal talking to him he mentioned his dog was a chesapeake bay retriever. both of us were like, "are you sure?" he said yes, his dog trainer said it looked like one and he looked it up on the internet and his dog was the "spitting image" of a chessie.
Only thing was, his dog was obviously an aussie. Curled tail, medium length hair, tipped ears, medium sized, same build.
Or how about people who don't even know what they have? When I worked in the petcare dept of Petsmart I sold crickets on a regular basis. While counting them out I always made small talk and asked what they were feeding. A commen answer was "a lizard". What kind of lizard? "oh, I don't know, it's about this big" and they show me with their hands how big it is, as if that's supposed to give me some clue.
A major pet peeve of mine, especially now that spring is coming up............ .is people taking animals out of the wild and trying to keep them as "pets". Mainly, at least when I was in MN it was painted turtles, and to a lesser extent, snapping turtles. They would come into the store and want to know how to take care of them. Of course the first thing I would do is say to let it go back where you found it. If they weren't willing to do that then I would tell them how to care for it. But most people don't realize not only how big of a cage they need, even as hatchlings, but how dirty they are and fairly difficult to keep in terms of frequency of water changes.