What I really hate is that every time I take a train (in Italy) I can be sure that:
1) the lady in front of me payed 30% less than me (OK, she is elderly and some discount may be fine)
2) the guy on my right payed 25% less than me (OK, he is a student, and has one of those cards)
3) the girl on my left has payed 45% less than me (OK, she has a special discount as a woman and booked the ticket in large advance)
4) the guy in businessman suit on the seat on the other side of the aisle has paid anyething between 50%, 80% or 100% less than me (OK, because he is an employee of the railway or of the government)
5) etc.
Simplified, I am the only one that is paying the full fare.