This is a Bad Comedian's Hat for the Fall of Cybertron deluxe Starscream figure! It is only meant for wearing in bot mode, but Starscream sure looks regal wearing it!
A tab on the back of the hat clips onto Starscream's head and makes sure it stays securely on.
This Hat has been successfully tested in Frosted Ultra Detail and that material is very much recommended. Take the usual precautions with this brittle material, though.