Easiest cosplay ever! This is based on the cover of volume 10 of the manga, which introduces Principal Kuno (hence the tropical/Hawaiian theme); the colors are a mix of the anime and manga versions.

Seriously, all cosplay should be this simple. I bought the hibiscus hair clip, lei, and conch shell at a costume store. The sarong is literally a piece of Hawaiian-print tied around me. I did nothing but cut the selvages off. Took about 10 minutes. ^^