When working in Egypt, once we had to call the "EGYPTIAN" Tech Service line for Hewlett-Packard. My Egyptian co-worker had a funny look on his face while talking.
When he hung up, he said: "That guy wasn't Egyptian. He was a Gulf Arab." He knew the accent instantly.
I've also read about some major heartburn from those millions of Muslims in Indonesia who don't know Arabic. They often feel condescended to by visiting clerics from the Middle East. Especially when those clerics insist that all REAL Muslims will learn Classical Arabic, so they can read the Koran as it was written.
You can also learn to speak Classical Arabic. But as I understand it, that's roughly the equivalent of walking around speaking in Shakespearean English, since Classical Arabic hasn't been updated since the 9th century or so. People might understand you, but they will look at you funny.
I learned a few Arabic words when I was in Saudi Arabia. But when I tried out those words on Egyptians, they looked at me funny. They could usually figure out what I was saying, but it took a few minutes. Then they would tell me the Egyptian way to pronounce whatever word I was mangling.
One of those words was "kwaji," which can mean either "foreigner" or "enemy." Or both at once!
Something that always cracks me up in Tom Clancy-type crap novels. At least since 2001, there's usually a line where Our Hero is described as speaking "perfect street Arabic."
Uh-huh. But if he's speaking Beirut street Arabic on the streets of Riyadh, he's going to blow his cover real quick.