If someone is sneery, they act like they are better than other people and make fun of them.
Sneery is not a nice way to act. It can make people feel bad.
Examples:
She gave me a sneery look when I fell down.
He has a sneery smile when he talks about other people.
The sneery girl laughed at my shoes.
The cat gave me a sneery look when I dropped my food.
The king's sneery laugh made everyone feel small.
The sneery boy always makes fun of others.