I speak American English.
Originally Posted by kompstar
1. What's with is a nonstandard idiom, so your rephrasing doesn't work. It sort of means explain. Some examples might help:
- You see a friend who always wears tee-shirts and shorts. But today he is wearing a suit and tie. You are surprised so you say: "Wow! What's with the suit and tie?"
- Your teacher, Mr. Niceguy, is usually a nice guy. But today he has been yelling at students for no good reason. After class, you say to a classmate: "What's with Mr. Niceguy?"
- Your sister knows that you hate cherries on top of ice cream. But today she gives you a bowl of ice cream with a cherry on it. So you say, "Hey, what's with the cherry?"
Again, that is very informal, nonstandard slang - but very natural and common. And it is always abbreviated, never what IS with.
It might help you to know that it comes from the more standard expression what is it with. Notice the word it there. Without the it it's wrong.
So it would be grammatical to say "What is it with you jacking my style." But it would not be natural, because the sentence is obviously casual, informal slang.
2. Jacking is slang for stealing - short for hijacking. In this case, it means imitating.