Design a mockup featuring a muscular model wearing a black 100% Cotton Men tank top Sleeveless cutout T-shirt Men vest in a gym setting. Provide split images of the front and back of the vest without showing the model's face. Customize the vest with your designs, ensuring they enhance and complement the muscular physique. Emphasize simplicity and clarity in the mockup, highlighting the unique cutout design and the fit of the tank top on the model's body.