Here is the New York Times mention of this trend in neckties
Novelty neckties are one of those things that are great in concept but terrible in reality. No self-respecting person could bring himself to wear a piano keyboard tie or something along those lines. I had a hard enough time convincing my dad to wear a very subtle novelty tie, one with a very tiny, practically invisible elephant motif.
Thus, these K-On! "rockties", like the Mio bowl or countless other moeblob goods, simply exist. I suppose you could hang them on your dorm doorknob to signal that you've a girl in your room.
Check out photos of the ties in the gallery, reserve yours for a modest 1900 yen at Hobby Search, or watch the video above and curse the goods-making gods for not having a castanet-themed version.