This area is tough on interacting with people. They are perceived as rude, but it is just shyness and afraid to make eye contact.
Many older folks appear to be grumpy! They might not be able to winter in Florida so they are just angry at the world.
Some folks feel they are rednecks (technically-too far north), they are just old county type people!(Take those rebel flags down! This is Yankee Country!)
I'm sorry you had an unpleasant experiance in Terre Haute. I'm guessing you didn't get off the beaten path and into town. I have lived here my entire life and the people here are the nicest people i have ever met. But i do agree, around Interstate 70 where the travelers are, they can be rude. But remember, they are tired travelers, not all are Terre Hauteans.