The two second flip is an easy way to fold a T-shirt quickly and efficiently. Lay a T-shirt flat on a table and draw an imaginary line width wise across the center with your finger, stopping you finger just at the edge. Pinch the fabric where your finger ends. Using your other hand, pinch the fabric at the shoulder exactly above where your first hand is. Then, cross your hand that is at the shoulder over to the hem of the shirt, still pinching the shoulder in your finger. Your arms should now be crossed. Still pinching the shoulder fabric, gather a bit of the hem fabric, so you are now pinching the shoulder point and the hem point between the same two fingers. You then need only uncross your hands to create a square, folded T-shirt.
Fold the T-shirt in half length wise, so you have a shirt that looks like it was cut in half from the neck to the bottom of the shirt. Then, fold the sleeves over to the front of the shirt and fold the whole shirt again, making the neck meet the bottom hem. This will create a flat, even square.
Folding the T-shirt in half widthwise gives you an easy foundation for folding. The shape of the shirt folded widthwise gives you a rectangle to work with. Then you just need to fold each sleeve over to make clean edges, and fold the shirt once more in half, heightwise, making a square.
Department stores often use a piece of cardboard to get a flat, folded T-shirt, and it's a technique you can use at home. Lay a square of cardboard at the base of a T-shirt laying flat on a table. Then, fold the neck over the cardboard so it meets the hem of the shirt. Next, wrap each side of the shirt over, pulling taut to make a crease against the cardboard. You can leave the cardboard in the shirt so it stays flat and is easy to stack with other shirts on a shelf.