When someone shows a bad attitude and is difficult to deal with.
Stroppinesses are usually not good because they make things hard for other people.
Examples:
Her stroppinesses make it hard to play with her.
I don't like his stroppinesses.
The teacher doesn't like stroppinesses in the classroom.
His stroppinesses make everyone laugh.
Her stroppinesses are the worst I've ever seen.
The cat's stroppinesses are funny.