The guy's name was LeMarshan.
We started a mission. He was only a level 4, but I figured I'd give him some practice and good money. As soon as the mission started, the screen asked me if I was sure I wanted to quit. I answered no.
I got in my car and the other guy suddenly died. Then he apparently appeared at the target location, which was almost three miles away, because it said he had reached the truck. Then he died again.
So I knew something was up and I wasn't about to let this jackass simply spectate while I made him money, so I let the enemies kill me ... even though, honestly, they shouldn't have shown up already (probably because he had teleported to the target location).
The mission FAILED and on the next job screen, I exited to go back to Freemode. And when I get back there, I get a warning about how leaving a mission early can result in being a Bad Sport.
Just another reason why Bad Sport is f*cking stupid.