('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'.
(..) Let's see what she does. Go in there. You'll miss it. Hold on a second. Lost your nerve? Tighten your seat belt. Where are you? We lost visual. Having fun? We must get out of this. Really? miles. Picking up speed. (..)1996 Twister