Just now, I was browsing Yorkie Talk, eating some McDonalds

I had a cheeseburger and Tobey totally snatched the last bite out of my fingers!!! He has NEVER done that kind of thing before. But I am worried because I think I have read that onions are bad for dogs and the cheeseburger had those little diced onions on it. I tried getting it out of his mouth but he jumped off the couch and ran away too fast! the little stinker!!!
anyway, should I be worried? If so, what could it do to him? I tried to search the threads but couldn't find anything really.... he won't die right??