기분 (mood) 나쁘다 (to be bad) means "To be in a good mood" (infinitive sentence). 100% correct would be 기분이 나쁘다 (marking the mood as subject of the sentence. if you want to say "I am in a bad mood" you can write: 기분(이) 나빠요.

We also say 기분 나쁘다 to mean "I am offended."