"You are bad."
Translation:आप बुरी हैं।
It's not so cut and dry. The choice of आप-तुम-तू is done based on factors such as age, familiarity, setting etc and not on the content of your speech. Use of तुम for someone older, even when in the middle of an argument, may seem crass and ill-mannered, reflecting poorly on you.
It also goes the other way. तुम is much more intimate than आप and if you suddenly start using आप with a friend, it may seem like you are distancing yourself from them