What's the meaning of the bold part
You want me to bust your head open?
I added the scene's picture from the movie (The fighter) to decribe the question better
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this communitybust your head (wide) open
is an idiomatic expression meaning to beat you up and give you a good pounding such that your head breaks open (figuratively).
Breaking a skull is a nontrivial matter.
Which is fairly significant.
You want me "to bust your head open"?
The man who is speaking threateningly is a boxer. The phrase means to break your head open by giving hitting or punching it.