('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'.
(..) All right, all right. Don't get all slobbery. No one likes a kiss ass. All right, hop on and hold on tight. I haven't had a chance to install the seat belts yet. Whoo! T People of DuLoc, we gather here today... to bear witness... (..)2001 Shrek