Pick a number between 1 and 5 (any number). Take that number and multiply it by 9. (They should have a two-digit number.) Take the digits from that number and add them together (example: 27 = 2+7=9). Take that number and subtract 5 from it. (They should now have an even number.) If A=1, B=2, C=3, and so on, have them assign a letter to this last number. Using the letter, ask them to think of a country in Europe that begins with that letter. Take the last letter of the country they chose and think of an animal. Finally, take the last letter of the animal and think of a fruit. Once they've done all of that say:
"The problem is, Kangaroos don't eat oranges in Denmark".
You will blow their minds and they will ask you how you did it and then you can say, "Because I know everything and I can read your mind which means I know exactly what was going on at that party you went to last night so don't ask me if you can go to another one any time soon".
Then they will look at you with guilt and you can send them to their room where they will believe they are being punished for whatever it is they did that they thought they got away with. You will have about 3 days before they try to pull the wool over your eyes again.