('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'.
(..) Okay. Cool. Thanks We'll just bring it up ourselves. I hardly think so. Why not? Well, we don't have a dolly, or lifting belts or any measurable upper-body strength. We don't need strength-- we're physicists. We are the intellectual descendants of Archimedes. (..)2007 TvShow: The Big Bang Theory Title: The Big Bran Hypothesis Season: 1 Episode 2