General Antonyms:
* Gloomy
* Sad
* Depressed
* Melancholy
* Sombre
* Serious
* Solemn
* Dour
* Grumpy
* Morose
* Unhappy
* Cheerless
* Gloomy
* Dispirited
More Specific Antonyms:
* Irritable: If someone is jovial, they are unlikely to be easily irritated.
* Hostile: Joviality implies friendliness, the opposite of hostile.
* Pessimistic: Joviality suggests optimism, the opposite of pessimism.
* Angry: Joviality suggests happiness and good humor, the opposite of anger.
The best antonym for "jovial" will depend on the specific context in which you are using the word.