Something that is maybe a bit annoying to most people but is very annoying or upsetting to a particular person.
Related to the word peeve meaning an annoyance or grievance, a pet peeve is something that a person has adopted(like a pet) to be extra annoying or upsetting to them. Like a pet, they pay a lot of attention to this peeve and may talk about it a lot and share funny pictures of it on the internet.
I know we aren't supposed to put fake names on the forms, but it's a real pet peeve of Rachel's, so make extra sure she doesn't catch you.
Tim: Why do the checkout clerks have to be so stupid?
Irene: I admit the conversation wasn't sparkling, but we got checked out quickly and efficiently, that's all that matters.
Tim: grr, I guess stupid people are just a pet peeve of mine.