a friend that you make on a airplane, seeing to it you will only see/hear from them once. after the flight is done, you most likely will not ever see or hear from this person again.
P1) you are a single serving friend, my man.
P2) What's that?
P1) When you become "friends" with someone that sits next to you on a plane.
P2) Oh well then, I guess i better get going cause the plane has just landed.
P1) aight, well then see yah around.