I highly recommend this book. It's well written and it gives a lot of insight into the Korean language and culture. These are some of my favorite idioms:
화장발/조명발 Cosmetic effect. Lighting effect- the girl( or man) only looks good because of the make-up or because of the lighting.
교편 잡다 - the love stick (the rod used to discipline students)
당근이지- That's the carrot- Of course! Right on!
고무신바꿔 신었다- She changed her rubber shoes- she found a new boyfriend.
필름끊겼다- My film stopped rolling- I passed out after heavy drinking.