Last October, my dog found a new bag of M&M peanut Halloween candy and ate like half of it. I told my vet and he said that it was ok. Milk chocolate is ok, it's the dark cooking chocolate that will kill them. FYI.
My family was in Ankara, Turkey back in '85. This was my fathers second tour over there. We we in Incirlik the first time. Anyway, there was a lady that lived on the top floor in our apartment building there. She had an Old English Sheepdog and fed him Peanut M&M's daily for treats. They never seemed to bother it.
I, like most people, always thought it was any chocolate that was bad for dogs.