미역국을 먹었어요 · 시험에서 미역국을 먹다
to fail (an exam), to be rejected (lit. to eat seaweed soup)
Example
열심히 준비했는데 면접에서 미역국을 먹었어요.
I prepared hard, but I flunked the interview.
Word parts
Seaweed is slippery, and 미끄러지다 'to slip' also means to fail an exam. A popular story also links it to 해산, meaning both 'disbanding' and 'giving birth' (after which mothers eat seaweed soup).
Good to know
Casual and humorous. This is why many Koreans avoid seaweed soup before exams and give sticky 엿 or 찹쌀떡 instead.