A computer convention was being held. On the train to the convention, there were three programmers and three engineers. Each of the programmers had his/her own train ticket. The engineers had only ONE ticket for all of them.
The programmers started snickering.

Then, one of the engineers said "here comes the conductor" and then all of the engineers went into the toilet. The programmers were puzzled. The conductor came aboard and got tickets from all the programmers. He then went to the toilet and knocked on the door and said "ticket please" and the engineers stuck their ticket under the door. The conductor took it and left, the engineers came out of the toilet a few minutes later. The programmers smiled and congratulated them on their clever thinking.

So, on the way back from the convention, the programmers had one ticket for the group. They started snickering at the engineers, for they had no ticket at all. Then, the engineer lookout said "Conductor coming!" All the programmers went to one toilet and all the engineers went to another. Then, before the conductor came aboard, one of the engineers left the toilet, knocked on the other toilet door, and said "ticket please."