I'm not the biggest fan of people in general, so this guy would have driven me absolutely nuts. But most of us (especially those of us who choose to spend lots of time in airplanes) live our lives in proximity to other people and thus have to deal with behavior that may annoy us -- loud cell phone conversations, body odor, drunkeness. (I've noticed that one behavior I often see that drives me crazy is people who bring three weeks worth of mail onto the plane and use the flight to sort through it. And instead of just making a pile of paper to discard -- perhaps out of privacy concerns -- they rip the paper into tiny pieces. So the entire flight I have to sit there listening to the sound of them tearing paper, which may sound innocuous enough until it continues for two hours.)

So your friend could have ruined this guy's day by getting him tossed from the flight, perhaps preventing him from getting home to his family or getting to work on time or getting to visit his sick mother in the hospital (see, for someone who doesn't like people, I can be quite compassionate!), or your friend could have dealt with this just like the innumerable other annoyances we all deal with on a regular basis.