I installed a 32x32 RGB LED Matrix Panel with 6mm pitch in the mortarboard of my high school graduation cap. With the help of a connected SmartMatrix Shield, Teensy 3.2, and a microSD card, I played various animations on the back of my (slightly offset) graduation cap. Power was supplied from a portable charger in the pocket of my dress (it had pockets!) with the power cables running down the side of my neck/tassel. I also replaced the button on top that holds the tassel with one made of a piece of clear plastic for better visibility of the LED image.
Some (cropped) photos from graduation. Process video coming as soon as I can find the SD card where I put all the footage.
This was a bit of a rush job, as we only got our caps and gowns two days before. I had a big panic moment where I thought I fried the Teensy the night before while modifying code. Turns out I forgot to select the right board in the Arduino IDE. I learned to (1) always order spare parts and (2) start things as early as possible and (3) double, triple, and sanity check yourself.