The absolute worst thing you can say to a Southern redneck. My friend Matt, a New Englander, was in a bar on Hiltonhead Island when a bunch of rednecks started harassing him. They asked him whether the capital of Kentucky was pronounced 'Louisville' or 'Louieville'. When he replied 'Louieville', they all started laughing at him. One of the guys pointed at him and shouted "That there Yankee's as dumb as a stump! The capital o' Kentucky ain't Louisville! It's Frankfort!" Matt turned to him and said:

"Yeah, who won the war, pal?"

Big mistake. All six guys stood up immediately. The bartender calmly explained to him to get the hell out, and Matt sprinted back to his hotel with six drunk guys lumbering after him. Once he got back, he locked the door and didn't leave the room for the rest of the night.