An idiot person who knows better, but does the wrong things just to see, knowing that it’s going to end up badly.
A person causing problems out of spite for sport.
A girl is out w/her friends and spots a male co-worker she hates, and he's w/his shorty, and flirts w/him so he would get in trouble.
Shorty would say.."Get your hands off him - quackadoo!"
A person who thinks they know everything, but don't know much because they don't have enough experience. Often talks to themselves and joins conversations they aren't welcome in, even if explicitly told to but out.