Since this is PET peeves, not "pet peeves", I've got one to share.
It's very annoying to walk my dog in an area that requires dogs to be on a leash (in particular, the towpath), and I've got MY dog on a leash, but then some people come down the trail and their dogs are NOT on any sort of leash. And they have three of them, two of which are waaaaay out in front of the owners so when the first dog comes right on up to my leashed dog, no owner in sight, and gets right in his face, well, my dog's kind of freaked out about it. They're not on a level playing field -- the other dog is free and easy and my dog is restrained -- and it puts my dog in what I guess you could call a socially inferior position. Then the SECOND loose dog comes up and now he's got two strange, large, unsupervised animals rooting around in his rear end.

And then finally the people show up and they're all friendly and laughing about it, third dog wandering close at their heels, like there's nothing whatsoever wrong with what they're doing. And this is at 2:00 on a beautiful Sunday afternoon when the towpath is simply dogtacular. WTF? I don't give a damn if you feel like, awww, it's so mean to keep my sweet little adorable Fido on a leash, he should be free to scamper and frolic wherever he needs to. Bullsh*t!!!! Be a responsible dog owner and LEASH YOUR ANIMAL IF IT'S REQUIRED BY THE PARK YOU'RE VISITING. There are signs that tell you all dogs have to be on a leash. And these were grownups who should've had better sense.

It was all we could do not to bitch-slap 'em.
End of rant. Next!