Like Jason's beloved Hot Rod, the Crazy Cube is an inexpensive and easy trick you can keep in your pocket and pester your friends with.
Tell the spectator to place the die in the small bottle with their selected number facing up (or down, which is what I prefer to tell them). Tell them to cap the bottle. Then, put the small bottle upside down into the larger bottle and cap it. Have them hold the jar. Look into their eyes, and after a non-creepy amount of time, tell them the number. You are right!
Here's a video: