Very good, grumbler. REAL BAD and SO BAD mean очень/так сильно and can be used in a positive or negative sense: I love you so bad. I want a new car real bad. He misses his children so bad.

So, would it be more correct to translate
Иногда мне по настоящему хочется сделать тебе больно
?

In this case, interestingly enough, bad can have either meeting because somebody couldn't be BADLY hurt, or someone could want to hurt you really BAD. So you can actually put down both translations :-)

OK, thanks. You do this if you wish - for the record.