My pet peave is people who run their dogs off thier leash in public areas. It's a form of cruelty too because their is often more danger to the animal than people understand.
One example was a couple of girls walking their golden labradore(without its leash) on a path in a section of reserved bushland. I was walking towards them with a very large german shepard on a leash, I called out to them to put thier dog on it's leash several times and got the response " It's ok he's a very friendly dog" and "he's very well trained he won't bite". I again yelled at them in a course manner to restain their dog which they ignored. I pulled the leash up as short as I could and tried to walk away but, the poor old labradore bounded staright for us. The end result was a rather nasty bite on the neck which crushed the spine and resulted in the labradores later death, it was all over in seconds.
These sorts of things occur because people are lazy and selfish,as much as they want their animal to enjoy freedom they neglect to think about the responsibillity they have to protect their animal and other people.
The other thing I think sucks is the overuse of people 'mercy killing' animals. I've seen many a pet recover from injuries that vets have said 'you should end its' pain now'. Basically the 'real' suffering is the owner watching the pet slowly die, no animal on the face of the earth except some humans wants to give up the struggle for life no matter how seemingly futile or painfull. The worst part is the decision to opt for the cheaper 'neadle' rather than life saving surgury even if it's just an outside chance.