One of the newer (well, newer to my kids) phrases is "Jinx". Whenever they both say the same word at the same time, one of them yells, "Jinx!". Then they can't say anything else until someone says their name.
But crafty little Jack recently put a new spin on the game of Jinx. I overheard Megan and Jack having a conversation the other day and when they both said the same word, Megan yelled, "Jinx!" Jack paused for a moment, turned to Megan and said, "You can't Jinx me. I have Jinx insurance!"