There is a technique to opening peanuts that few people seem to know. We put together this video to demonstrate an easy way of opening a peanut. You can do it with one hand.
The first thing to do is to make sure that the peanut is oriented correctly. You want to find the slight hook at top of the peanut (see red arrow). We'll start by placing our thumb along the seam of the peanut just below that hook and pressing until the shell just barely cracks open.
Next, we move our thumb slightly lower to the bottom of the two bulges of the peanut, and press again. This should force the initial crack to open wider. We then put our index finger at the top of one half of the shell and pull it open.
As always, a video helps in this. Either click on the link above, or click on here to see this technique in action.