1. superlative form of hissy; most inclined to hiss or make hissing sounds
Usage: informal; often used in the phrase 'hissy fit'
2. superlative form of hissy; characterized by the most anger, irritation, or dramatic complaint
Usage: informal; colloquial

Examples

• The cat was the hissiest of all the animals in the shelter.
• She threw the hissiest fit when she didn't get her way.
• That snake is the hissiest one I've ever encountered.
• He became the hissiest version of himself after losing the game.
• The hissiest complaint came from the customer who waited longest.