('chiefly US') cities in the 'Rust Belt' [=an area formerly known for industry and manufacturing]
When you're riding in a car, you should always 'belt up' [=('US') 'buckle up'] for safety.
That remark was 'below the belt'. = That remark really 'hit' (him) 'below the belt'.
(..) Because l can take you to your son. Yeah, right! No. l know your son. He's orange. He's got a gimpy fin on one side. That's Nemo! Fasten your seat belts! Everybody hold on! Too loud. Too loud for me. Twinkle, twinkle little star Find a happy place. Darla, your uncle will see you now. (..)2003 Finding Nemo