Our vet told me that different dogs have different tolerances to these things. Also, he said that with things like coffee/coffee grounds and onions, it depends on the amount they gget a hold of. He said that most won't like the taste so if they are getting in the garbage, for instance, they might get a little of the coffee grounds, but they are really going for the table scraps. That makes sense, but I had an acquaintance whose cat got into a little bit of potato salad and the small amount of onion in that killed the cat. The vet verified that it could not have been anything else. My aunt gave her small dog leftover ham and the dog died- again, her vet verified that it was the ham.
I had not known about grapes and raisens until the vet and I had this discussion a month or so ago. I think he also mentiioned cranberries but I'm not positive. Grapes stuck out in my mind because I had given a couple to one of my dogs before. I try to take note about stuff like this since a had a very beloved dog once that I fed a lot of table food (cooked, healthy for humans) to and he became diabetic at 3 years old. I was told that he probably had a genetic predisposition and the food I fed him obviously didn't kill him but it caused his pancreas to quit functioning normally and it stopped secreting insulin. After spending 7 years of giving him urine tests and shots of insulin twice a day, I try not to take the chance anymore.