Something I've been noticing more and more in normal games...

I guess I'll preface this by describing how this behavior manifested itself in a game I played less than 10 minutes ago. I entered into champion select as soon as the option appeared and quickly selected Karthus and typed "mid please" in chat. About 5 seconds later, someone who had been in select the whole time selected Karma and instantly locked. I assumed he was supporting, but as the countdown began he started talking about how he was mid. He justified this (which I called trolling) by saying that I hadn't locked in yet and so didn't have any right to go mid. He went on to feed, but that's another matter entirely.

While I understand that this is only an isolated incident, I was compelled to make a post on Reddit because it was the third game in a row where someone has done this. Furthermore, over the past few days I've seen this excuse used a dozen of times. I really don't remember anything like this from the hundred or so games I played in season 1. Since when did people start viewing insta-locking as the only way to really call a role? I don't want to start doing it, but at this point it seems like the only way I can actually avoid being extremely annoyed by duo mid/jungle/top.