('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'.
(..) Ow. - Don't make me laugh. - All right. Oh, you'll protect me? Yeah. I have a black belt, you know? Nightmares-- It's fine. Shh. Oh, fuck. Hey, what are you doing, little guy? (..)2008 Two Lovers