Two games in a row I was lobby leader, I join say "I'd like mid please" and someone just gets in before me, 2nd last pick. I said "I'm going to take mid"

They abuse me, say two mid two mid ok noob blahblah and swear. I pick my mid, then they 2nd last pick a mid and continue to troll. Someone que dodged just in time, I rejoin same guy same story.

What can I do here?

You should let the person who called it first take it. There is no current method of rolling some dice to see who wins, and the meta is the meta.

If you really want to practice, play blind pick and pick as fast as possible.

Otherwise, copy the text you want "MID AP Ahri," and then click the text box once you join the champ selection screen. If you press Ctrl-V fast enough and press enter before anyone else, you too can have the choice to go where you want.

Past that, you are poop out of luck.

Just play double ap.

Don't dodge and pray for a miracle. I usually treat these games as 'practice'.