Why you always busting my ass?

I'm learning expressions from the movie, Pearl Harbor.

Here are two best pilots flying their own planes.
One suggests they play chicken.
The other one, unwilling to do it, refuses and says.

'Why you always busting my ass?'

And then he ends up playing chicken with him.

Not exactly knowing what that means, I looked up the dictionary which says

To bust ass is to fart. BUT if used with a possessive, it means to work hard.
Also often used with a possessive and immediately followed by an infinitive

I just busted ass and it smells real bad.
You better be busting your ass if you want to finish the job on schedule.
I was busting my ass to finish my homework on time.

http://www.urbandictionary.com/define.php?term=bust+ass

Neither farting nor working hard doesn't really seem to fit in the context though, I assume.
My guess was 'bust one's ass' is tease someone or pick on someone.

This is the video in which the expression 'bust one's ass' is used.
Could you please take a look at this?

https://www.youtube.com/watch?v=9YSzAawigiI

The actor mentions that at 0:35.

Now what would be the meaning of 'bust one's ass'?

I'd appreciate any comment from you.
Thank you in advance.