Yep, a t-shirt with a fully functional graphic equalizer embedded on the front. It changes with the music around you, and even reacts to conversation! $39.99 from Think Geek. Link -via Everlasting Blort
My friend wore one of these to an MC Chris show, and was promptly dragged up on stage to rock out with his EQ out. Epic win for g33k couture, epic fail for the paltry t-shirt electronics. Loud concert monitors + limited sensitivity t-shirt electronics = maxed out bars for the whole show. Oh, well.
Unfortunately, it's not 'fully functional' at all. It only responds to the amplitude of the sound, not the frequency, and only has a few 'levels'. The multiple columns are only for looks.
My friend had one and the battery pack actually set on fire.
You can get other sound reactive designs aswell.