I guess my biggest "pet" peeve is when my cat doesn't use the litter box!
Seriously, I try not to have pet peeves, yet I do. My number one would be drive by posters that didn't take the time to ask questions here on the forum. Yet, through some miracle they find us to post a rant.
My number two is people that have one thing go wrong on their cruise, and then they start looking for any thing else they can complain about. "My cruise was awful, everything was terrible".
That is with the assumption the pet peeves were about the forum posts. I can make an extensive list of peeves about how people behave onboard the ships.