Zoro usually maintains a very stern, serious, and distanced personality, but often loses his temper in a goofy and exaggerated comical style. It would seem, however, that this anger is the only emotion that Zoro often feels comfortable showing. 

Outside of situations where he feels confident in battle, he tends to smile or laugh the least out of the Straw Hats and rarely fools around with the rest of the crew, and likes to distance himself more to sleep or train.