When your parent works with animals and many different types of people, there is always a story. And from that, we learn how animals of all kinds work and what you don't give them. But I'm willing to let some of it slip.
1. Give them table food
I know it is tempting to feed your fur children what you are eating, but it doesn't help their digestive system or encourage good behavior. Treats are fine, but your pork chop is not.
2. Dress them up in confining costumes
I go weak for small dogs in cute costumes, but there is a limit. They should be able to move all of their legs and walk comfortably. So, be reasonable.
3. Miss vet appointments
They spend years in school to work on animals and work odd hours sometimes to make sure your animals are healthy and taken care of. Unless you have canceled your appointment, try to show up when you said you would. Don't waste people's time.
4. Assume you know more
*pfft* Do not think google has any and all answers to what is going on. There are similar symptoms and actions for multiple things. Ask your vet and listen.
5. Criticize product prices
Look, I know it is a lot. And, yeah, there are some bad apples in this profession. But most vets try to stay reasonable and stay afloat. It's not their fault medicine, and pet protection is beyond what you thought.
6. Ignore fleas and other pests
You wouldn't let a kid spend a week with lice, so pay attention to what your pet is doing. A sign of something biting them is when they bite at something in their fur, but is among others. Keep an open eye on their behavior.
7. Not vaccinate
Pets are like children, and we need to make sure they live healthy lives. Do yourself a favor and treat them so they don't suffer too much from things that can be avoided.
8. Ignore weather conditions
This angers me to no end. If it is too hot or cold to walk your dog, go earlier or find other exercises. An animals paws cannot take hot concrete, and no animal should freeze to death. Animals are not accessories; they can stay at home. (Yes, I will break a car window if an animal or person is about to die.)
9. Not control your animals
The vet is never fun, I'm aware. But keep your animals under control. They don't like being on a leash and want to run? Tough. The office you are in is not a park. Be respectful. Also, if a vet asks you to hold them, please, hold them.
10. Put them on human diets
Under no circumstances are your pets vegetarians or vegans. They need meat and certified food. Don't try to kill them. Maybe control food portions and when they eat (I.E. three times a day), but no other nonsense.
11. Not spaying/neutering
Ever wonder why we have over population in many areas? Well, it is because non-breeding owners and bad pet parents do not prevent more breeding when it is time to. Get this done for the animals sake. It helps prevent further shelter overpopulation also. (Adopt, don't shop.)