If someone does something snottily, they do it in a way that shows they think they are better than others.
Doing something snottily is not nice. It can make people feel bad.
Examples:
She snottily told me she was better than me.
He snottily said he didn't want to play with us.
They looked at us snottily.
She snottily said she didn't like my drawing.
He snottily told me he could run faster than me.
They snottily said they didn't want to be our friends.