Like a lot of the words we use, "extra" doesn't seem to have a clear inventor. It's like we went to bed saying that people were "doing it up" or "doing too much" and woke up just calling them extra instead.
It works, though. It was a little hard to tell whether people meant "doing too much" in a good way, so I would probably just say, "Oh, sorry," and then get laughed at if someone said that to me.
Normally, I'd be happy to break down what "extra" actually means, but I'm afraid I can't because these people just redefined it, again and again.