I was golfing yesterday with a couple of friends and one asked the other if it was his shot or Mikes. The way he asked was: "Is it you or I, Mike?" Shouldn't it be:"Is it You or me, Mike?"
Your friend is correct- traditional grammarians argue that we should use the subect case after the verb 'be', though the vast majority use the object. It can be done and pedants the world over will be reassured to hear that some people are using the form, even though they are a tiny minority. The reasoning behind it is that 'be' is a copular, or linking, verb abd therefore doesn't take a object.