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A: Come on in.

B: Yeah, time to get my swerve on here.

What you drinkin', dog?

A: What am i drinkin'? The best.

B: The best. I know. It's the best for the best.

A: I heard you had a beef in vegas.

There's a green light on your ass.

B: Nah, no problem. It's all good.

It's a dialogue in the Training Day, I don't know what any of the three means, can someone explain them to me and are they used only in American English?

Thanks.
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I have never used or heard swerve used that way, and I assure you I have never said nor heard there is a green light on anyone's ass. So while they sound American, they are not common American phrases -- at least, not among the people I know.

Beef, however, is reasonably common, although I've never heard it used to mean a fight. Just a complaint.
Comments  
A: Come on in.

B: Yeah, time to get my swerve on here. (to party hard /to flirt )

What you drinkin', dog?

A: What am i drinkin'? The best.

B: The best. I know. It's the best for the best.

A: I heard you had a beef in vegas. (fight)

There's a green light on your ass. (it probably means that he is wanted by a rival gang/police)

B: Nah, no problem. It's all good.
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time to get my swerve on here -time to get my groove on, time to flirt and have fun
I heard you had a beef in vegas - I heard you had a fight, a grudge in Vegas
There's a green light on your ass. - they're looking for you

As much as BrE and AmE are related and exchanging vocabulary I would call these American Slang.
By the way, green light (or greenlight) is not slang per se. It's used in general talk and newspapers to mean "permission".
 BarbaraPA's reply was promoted to an answer.
Frankly, I find them totally weird! I will probably be in splits if I anyone tells me they have a green light on their ass!! Emotion: big smileEmotion: big smile
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Well you'd have to be living in an NY ghetto to hear people speak like that really. Or you'd have to be the opposite..someone like 50 cent or Dr. Dre Emotion: big smile