Instructions: 1. Make a skin on Blockbench. 2. Duplicate the skin's texture. 3. Import the costume "DiamondArmorPrank" inside the project as a texture. 4. Copy the armor texture and paste it on top of the duplicate skin. 5. Now it will look like the skin has full diamond armor! 6. Open a new Minecraft world, with the no armor skin. 7. Invite your friends, and then go mining. 8. Change your skin to the diamond armor one. 9. Come back to your friends after mining for a short amount of time (1 or 2 minutes is enough) 10. It will look like you have full diamond armor!
The diamond armor textures are by Mojang/Minecraft.