Obstropolous
A person who makes life a nightmare just because they can. They're like a toddler with a swear word and a middle finger.
My neighbor is obstropolous. He yells at the mailman every day just because he feels like it.
My mom is obstropolous. She won't let me eat cereal for breakfast unless I do 10 push-ups.
My teacher is obstropolous. She gave me a pop quiz on a holiday just to mess with me.