The UK's National Rail used to have a "4 for 2" offer. Four people could travel together with a 50% discount if booked in advance. One day our friend was ill b

The UK's National Rail used to have a "4 for 2" offer. Four people could travel together with a 50% discount if booked in advance. One day our friend was ill but three of us weren't going to miss the only sunny day of British summer so we went without him. The ticket agent on the train was quite insistent that we were breaking the rules...and I guess in some sense we were, as the tickets did say four people had to travel together. We ended up with a "One time courtesy exception" so we could continue our journey. National Rail later revised the program to a 33% discount for groups of 3 or more.