What does 'freaking bad' mean?

In the song Billionaire the singer says 'I wanna be a billionaire so freaking 

bad...' So, what does the highlight expression mean? 

Well, it means you are desperate to become a billionaire. The expression 'freaking bad' adds even more emphasis to your wish. Look at this:  

'freaking' = overly emphasized really

Other words like freaking:
Wicked
Mad
Hella
Super or Super duper
Uber (german word for 'over/really' that has been incorporated into American English)

the sentence "I wanna be a billionaire so freaking bad" can be rewritten as:

I wanna be a billionaire wicked bad.   

I wanna be a billionaire hella bad.

I wanna be a billionaire super/super duper bad.  

I wanna be a billionaire uber bad.

"Mad" does not really make much sense in the sentence you provided even though it means basically the same thing as all the words above. example of a use of 'mad':

It is mad cold outside = It is really really REALLY cold outside.

Source(s):

Native Speaker of American English 

See ya!

Josete