To behave badly means to act rudely or in inappropriate ways. It involves breaking rules, showing disrespect, or causing trouble.
There can be no question of holding forth on ethics. I have seen people behave badly with great morality and I note every day that integrity has no need of rules. Albert Camus
People often behave badly when they are trying to prove a point. Iain Banks
All writers behave badly. All people behave badly. Claire Tomalin
Any time there is a lot of money or ego involved, people tend to behave badly. Brad Grey
Generally speaking, rural drivers are a much better behaved species than city drivers. I'm not sure whether they're intrinsically this way, or there are just fewer opportunities for them to do behave badly. You can't go around running red lights if there aren't any red lights to run. Linwood Barclay
Cats do not give us too many chances. Abuse a cat's trust twice and you could be history, for cats are much less forgiving than dogs and will often lose their trust in you should you behave badly. A dog gives you infinite slack; not so a cat. Jeffrey Moussaieff Masson