If you want to do this with a shirt on, the easiest way is with a button down shirt. Just undo one of the buttons a few down from the collar, so that your can stick your hand through the opening in the shirt.
You don’t have to move your arm much for this to work. It should be a small movement, starting with your upper arm near your side and your forearm across your chest.
You can do this with a shirt on if you stick it in through the collar.
