By taking one hand in the shape of a karate chop and slicing it down on your other hand's palm is the visual representation of being chopped, making it easier for those around you to understand how your feeling.
Mitch: Yeah dude, that was a fat ass blunt we smoked
Jerrica: Hell yeah nigga, how you feelin greg?
Greg: *makes a chopped hand motion* im fuckin chopped like... fuckin chopped.
Marty's MX5 got chopped by Moog's S2000 that is powered by unicorn farts.