('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'.
(..) Don't listen to them. Okay, I think you're manly for what you did. And when the hours and one second is over, I'm gonna loosen your belt, then take off your pants... - No. - Then your underwear. No, no, stop. - Then suck your lollipop. (..)2016 TvShow: Shameless Title: Swipe, Fuck, Leave Season: 7 Episode 2