I think some of those things are okay...in moderation. Many people feed their pets cheese, or even buy commercial products that contain cheese. Tuna, I think would go the same for pets as people, TOO much would mean high levels of mercury, but a little here and there, not a problem (except for Gucci, she throws up canned fish
) Ham, well, it has alot of nitrates and salt, and they say most dogs can just expel excess salt, unlike humans that retain it, but if the dog has any liver, heart or kidney problems, they need to be on a sodium restricted diet, usually under the guidance of a vet. Gucci doesn't like ham, so that one is easy. lol
Potato peels are dangerous if they are green or have "sprouts" on them, because of a certain toxin that develops, if the peels have no green or sprouts, they are fine... But I guess they would rather just say "potato peels" than explain why, which I guess is better than the last list that listed "potatos" as being bad.
Avocados, are mixed. Some people feed them, some don't. There is an ongoing debate about them over at the K9Kitchen group.
I use a little garlic in Gucci's diet, and she is fine. She prefers parsley or cilantro leaves, but sometimes I don't have those in the fridge and want to add a little flavor, plus...I read it keeps the fleas, ticks and mosquitos away. But again, too much of it is controversial.