If you want to stand out in a geeky party take a look at this project. This is super duper simple pendant made of Attiny4313, 5×7 Led matrix and couple other necessary components like resistor, button battery and push-button.
It appears that Attiny4313 microcontroller pins perfectly lines with Led matrix pins so it can be soldered directly on back of it. No PCB is required. Power supply problem is nicely solved by using two wires as necklace where battery is simply hidden behind person. Push button is used to change display modes where various animation effect may be selected. Satisfaction guaranteed.