Cowboys "drive" cattle to market by forcing the cattle to walk/run in the direction of the market. My friend was suggesting getting in the head of a cattle and driving it like a car.
When I was in seventh grade, we were reading a story set in a submarine and the teacher was talking about how it is hot in there and there are no doors. Someone said "They could just roll down a window." (He was joking, not stupid)
Same guy commenting on why a steer is called a "head of cattle" (Texas History, about the Alamo) said "Just think, drive a head of cattle to market can have an entirely different meaning."