Things I do that aggravate my wife so much, (she's from Dallas, TX).
I will ask for a "coke" just to see if they go, alrighty, will that be a sprite, Dr Pepper, etc...(in the south, if you want a Coke, you need to say Coca-Cola)

Ask if they have regular Iced Tea....(most places will bring you sweet tea if you just ask for Tea)

And the sayings they have, getting them to say y'all, or youins....it just makes my travels so much fun. I'm not making fun of the people, it's just funny to me how much different the dialect is in just a few hours drive.