The flag is battle flag of the Army of Northern Virgina. I can only guess based on the kid’s quotes, but it looks like — given that “rednecks” aren’t limited to the South — that he is using as a self description. You know, like how you can call your sister a name, but you beat up the kid who calls her the same name. It’s OK when you do it. Like when black people call each other nigger.
I'm sure he is. But the casual observer might see it as reinforcing some negative stereotypes like I said. Still if he wants to fly it then he should be able to, regardless of what people think. There may be a constitutional right to be stupid but so far as I know there is no constitutional right not to be offended.