There were three friends from IIT Madras and three from Anna University, Chennai. They were stranded at the Pune Railway station and were on their way back to Chennai.
So the first part of the journey was from Pune to Bangalore by train. The Anna people bought three tickets. The IITM people bought only one ticket. When the Ticket Checker came by, the IITM people all went inside a toilet and put the ticket out. So they got away.
They all got off at Bangalore. The Anna people were a little pissed after the incident. This time, they bought only one ticket. The IITM people didn't buy any. When the Anna people went and hid inside a toilet, one of the IITM people knocked on the door. Out came the hand and the IITM people took away the ticket and headed for the opposite toilet.
They all got off at Chennai Central. The Anna guys barely managed to make it there. They were now very pissed. The last part of the journey was from Chennai Central to Guindy station by suburban rail. This time, the Anna people decided not to buy tickets at all. The IITM people bought three tickets.
Unfortunately, there are no toilets in Chennai suburban trains!