Someone who is labeled as being a 'potential terrorist' (usually due to their skin color, clothing etc) but in a less accusing, more ironic way.
A comedic sleight on post 9-11 paranoia, saying someone is a Casual Terrorist is simply implying they look like a stereotypical terrorist, even though you know they are not one and are probably just trying to earn an honest living.
Person 1: Hey look at Ahmed sitting there in his taxi, I wonder if he's planning on blowing up any buildings today?
Person 2: Haha, naah he's too busy picking up customers and earning fares.
Person 1: Yeah, he only does that sorta shit on an off-day. He's a Casual Terrorist.